From The History of Philosophy: A Short Survey by James Fieser

Home: www.utm.edu/staff/jfieser/110

Copyright 2008, updated: 1/6/2017





A. Descartes

Methods of Investigation

Systematic Doubt

The One Foundation of All Knowledge

Spirit-Body Dualism

B. Malebranche

Sensory Information: Viewing through God

Bodily Movement: God causing all Physical Motion

God and Evil

C. Spinoza

God as Nature: Substance Monism

Determinism and Human Bondage

Free Speech

D. Leibniz

Monads in an Infinitely Divisible Plenum

Perception, Appetite, and Mirroring in Monads

Dominant Monad Souls and Parallelism

Evil and the Best of All Possible Worlds

Reading 1: Descartes on Doubt and Certainty (Meditations 1 and 2)

Reading 2: Spinoza on God not Willfully Directing the Course of Nature (Ethics, 1, Appendix)

Study Questions


Rationalism is the philosophical view that knowledge is acquired through reason, without the aid of the senses. Mathematical knowledge is the best example of this since through rational thought alone we can plumb the depths of numerical relations, construct proofs, and deduce ever more complex mathematical concepts. We can even envision that someone locked in a room with no sensory experience whatsoever might still arrive at a sophisticated level of mathematical knowledge. Several ancient and medieval writers held to rationalism, most notably Plato and philosophers who followed in the Platonist tradition. In the mid 17th century, though, rationalism was given a unique twist by philosophers who held that our most important mental concepts are innate—or inborn—and from these we deduce other truths with absolute certainty. Advocates of this position were largely from the continental European countries of France, the Netherlands, and Germany, hence this new breed of rationalism is often called “Continental Rationalism.” The main philosophers associated with this movement, which we will explore in this chapter, are René Descartes, Nicholas Malebranche, Baruch Spinoza, and Gottfried Willhelm Leibniz.



René Descartes (1596–1650) was born in the French city of La Haye en Touraine, subsequently renamed “Descartes” in his honor. At 11 years of age he entered a Jesuit college, and by age 20 earned a law degree according to his father’s wishes. While this education pleased his father, a high-court judge himself, Descartes never actually did practice law. Shortly after graduation he abandoned all study, and, disregarding his personal conviction that military life was idle and cruel, and became a military engineer for the purpose of traveling, seeing the world and discovering truth found both within himself and in “the great book of the world,” as he described it. He sold all of his possessions and invested the funds, along with money from an inheritance and from patrons, which allowed him the privilege and freedom to travel and study most of his life. Specific direction for this came during his time in Europe when on three occasions Descartes dreamed of becoming a scientist and philosopher. At that point, he followed his dreams—literally. His most fruitful time as an author was during his 20 year residence in the Dutch Republic where routinely stayed in bed writing until around noon. While he valued his privacy, and regularly changed residences to protect it, he nevertheless gained international fame through his writings. He became as renown in science and mathematics as he was in philosophy, and his publications reflect this diversity. Descartes never married, although he fathered children and rationalized that, after all, he had never taken a vow of chastity. Invited to become teacher to the 22-year-old Queen Christina of Sweden, Descartes’ daily routine was dramatically altered and he rose at 5:00 a.m. to instruct the demanding queen in philosophy. In addition, she ordered him to write a ballet in verse. When he died of pneumonia one year later at age 53, it was speculated that this pressure and inconvenient schedule was the underlying cause. Alternatively, some suspected that he contracted the disease while nursing a French ambassador with pneumonia back to health.


Methods of Investigation

Like other thinkers of the time, Descartes was attracted to the notion of a scientific method of investigation, which when followed would enable him to make new discoveries and push the boundaries of knowledge. Thus he devised his own method, the starting point of which is to eliminate all former opinions and establish knowledge afresh only on solid foundations. According to Descartes, the knowledge that we typically attain through education and life experience is an unsystematic mixture of truths and falsehoods, and it is often impossible for us to easily distinguish between the two. It is similar to the disorganization and poor layout that we see in old cities as they slowly expand from small villages to large urban areas, randomly adding one neighborhood after another. While we might try to improve the matter by inspecting our knowledge-base one fact at a time, this, he argues, will not do, and the only trustworthy way to proceed is to brush it all aside and start again. Similarly, the most organized cities are planned by a single architect from ground up, and this is the model that we should follow when expanding our knowledge.

            Thus, Descartes says, we should being by clearing away our old and disordered schemes of knowledge. After that, we should follow four specific rules of inquiry that will enable us to methodically build a coherent system. Rule 1 is to accept only indubitable, clear and distinct ideas. He describes here his own experience when applying this rule:


The first of these was to accept nothing as true which I did not clearly recognize to be so; that is to say, carefully to avoid precipitation and prejudice in judgments, and to accept in them nothing more than what was presented to my mind so clearly and distinctly that I could have no occasion to doubt it. [Discourse on the Method]


His point is that the foundation of his knowledge should be only facts that he knows with certainty and which he can recognize as such because of the clarity and distinctness that they display. Rule 2 is that, when trying to solve problems, he would “divide up each of the difficulties which I examined into as many parts as possible, and as seemed requisite in order that it might be resolved in the best manner possible” (ibid). Once the problem is broken down into smaller units, he proceeds with rule three that he should begin with the simplest objects, and work to the harder and more complex ones. Finally, Rule 4 is to review: “to make enumerations so complete and reviews so general that I should be certain of having omitted nothing” (ibid).

            Descartes recognized that if he actually began by rejecting all of his previous views, he would be temporarily entering a no man’s land in which he could believe or trust nothing until his final system of knowledge was well underway. During that time, though, how should he behave? Should he become an atheist, a drug peddler, or bank robber? To address this concern he established a provisional code of morals that he would follow, which would hopefully keep in on the right track until he completed his system of knowledge. First, he would obey the laws of his country and adhere to his faith in God. Second, he would be consistent in following positions, even if they seemed doubtful. Third, he would focus on changing his desires rather than attempting to change the world because of his desires. Finally, he would choose the best occupation he could, which he determined to be that of a philosopher.


Systematic Doubt

Once establishing his method of investigation, Descartes proceeds to build a system of knowledge that he can trust with absolute certainty. The first step is for him to clear away the unreliable clutter of his previous belief system. To that end he uses a systematic doubting process that would plow away any previous belief he held that was the slightest bit questionable. He writes,


It is now some years since I detected how many were the false beliefs that I had from my earliest youth admitted as true, and how doubtful was everything I had since constructed on this basis. And from that time I was convinced that I must once for all seriously undertake to rid myself of all the opinions which I had formerly accepted, and commence to build anew from the foundation, if I wanted to establish any firm and permanent structure in the sciences. [Meditation 1]


The type of doubt that Descartes describes here is not a common sense doubt, but, instead, an exaggerated systematic doubt. For example, common sense tells me that I should doubt reports that creatures have visited earth from other planets, or that a house is haunted, or that some people can see into the future. Descartes, though, wants to move well beyond this kind of doubt and question things that are even commonsensical. My common sense tells me that the ball in front of me is red, but what if I’m colorblind? It’s unlikely, but as long as there is some reason to doubt it, I should. Thus, his rule of thumb at this stage is that if it can be doubted, it should be doubted. The point of this exaggerated doubt is that, once we clear away everything that’s the slightest bit questionable, we’ll only be left with truths that are certain.

            As he casts his doubtful eye on questionable beliefs from his past, he realizes that it would be impossible to inspect each of them one at a time; there are just too many. Rather, it is more efficient to submit to inspection the underlying foundation of the bulk of his beliefs. He writes,


Now for this object it is not necessary that I should show that all of these are false -- I will perhaps never arrive at this end. But inasmuch as reason already persuades me that I ought no less carefully to withhold my assent from matters which are not entirely certain and indubitable than from those which appear to me evidently to be false, if I am able to find in each one some reason to doubt, this will suffice to justify my rejecting the whole. And for that end it will not be requisite that I should examine each in particular, which would be an endless undertaking; for owing to the fact that the destruction of the foundations of necessity brings with it the downfall of the rest of the edifice, I will only in the first place attack those principles upon which all my former opinions rested. [Ibid]


What is the underlying foundation of most of his beliefs? It is the senses: “all that up to the present time I have accepted as most true and certain I have learned either from the senses or through the senses” (ibid). Drawing on the arguments of ancient Greek skeptical philosophers, Descartes gives three arguments for why we might doubt the senses. First, we regularly experience sensory illusions, such as when things at a distance appear much smaller than they really are. While this is a problem, Descartes argues that it is not a very big obstacle, since we can get used to sensory illusions and trust our senses for more important things. Second, the reliability of my senses is undermined when I consider the possibility of whether or not I’m dreaming. I look at the ball in front of me and my senses tell me that it exists. But, if I’m dreaming, then this experience is completely unreliable. It doesn’t make any difference if it really feels to me like I’m awake, since many times I’ve had dreams in which I was convinced I was actually awake. Descartes agrees that this too goes a long way in undermining the reliability of our senses, but not completely. For example, it allows me to doubt whether the ball in front of me actually exists, but it does not entitle me to doubt whether the three-dimensional world itself actually exists. To have even a dream-like perception of a round ball, according to Descartes, there must at least be a three-dimensional world which is the source of my dreams about three-dimensional shapes.

            The third reason for doubting the senses is one of Descartes’s claims to fame: what if God, or some evil genius, is deceiving me about everything, including the existence of the three-dimensional world? Perhaps everything that goes on in my mind is the result of a divinely-implanted hallucination. That would cast doubt on virtually every belief I have, including whether I even have a body:


I have long had fixed in my mind the belief that an all-powerful God existed by whom I have been created such as I am. But how do I know that he has not brought it to pass that there is no earth, no heaven, no extended body, no magnitude, no place, and that nevertheless they seem to me to exist just exactly as I now see them? And, besides, as I sometimes imagine that others deceive themselves in the things which they think they know best, how do I know that I am not deceived every time that I add two and three, or count the sides of a square, or judge of things yet simpler, if anything simpler can be imagined? . . . I will then suppose, not that God who is supremely good and the fountain of truth, but some evil genius not less powerful than deceitful, has employed his whole energies in deceiving me. I will consider that the heavens, the earth, colors, figures, sound, and all other external things are nothing but the illusions and dreams of which this genius has availed himself in order to lay traps for my gullibility. I will consider myself as having no hands, no eyes, no flesh, no blood, nor any senses, yet falsely believing myself to possess all these things. [Meditation 1]


Not only does the evil genius hypothesis cast doubt on the very existence of the three-dimensional world, but it also calls into question the confidence I have in my ability to do mathematics. Thus, when I consider that 1+1=2, perhaps the evil genius is just making me think that it’s true when it in fact isn’t.


The One Foundation of All Knowledge

It’s important to emphasize that Descartes himself was not a skeptic, but just used this powerful skeptical doubting device as a means of clearing away his older and more insecure beliefs. With those out of the way, he goes on to discover some firm belief which even the evil genius can’t make him doubt. All it takes is one truth, he argues, and that then can serve as the foundation for building an elaborate system of knowledge. As the ancient Greek mathematician Archimedes once said, “Give me a fulcrum and a lever and a firm place to stand, and I alone can move the world.” Indeed, Descartes finds one such belief that even an evil genius cannot make him doubt: the truth that he exists. He writes,


[Suppose that] there is some deceiver or other, very powerful and very cunning, who ever employs his ingenuity in deceiving me. Then without doubt I exist also if he deceives me, and let him deceive me as much as he will, he can never cause me to be nothing so long as I think that I am something. So that after having reflected well and carefully examined all things, we must come to the definite conclusion that this proposition: I am, I exist, is necessarily true each time that I pronounce it, or that I mentally conceive it. [Meditation 2]


Descartes’ reasoning here is that in order for him to be deceived by the evil genius, he must exist to begin with; this is the same argument that Augustine offered centuries earlier when attempting to show that there is at least one truth that we can be absolutely certain of. In one of his publications Descartes expresses this idea with the phrase “I think, therefore I am” (in Latin, cogito ergo sum). Later on, though, he rejected this expression since it sounded like he was drawing a logical conclusion—and this is a problem since an evil genius might be deceiving him about the reliability of logic. Rather than being a logical inference, the truth of his existence is something that he can immediately grasp “by a simple act of mental vision” (ibid, “Replies to Objections”).

            This is exactly the foundation Descartes thinks he needs upon which to build his system of knowledge. How he proceeds in his building project is somewhat complex, but his basic strategy is to shoot down the evil genius hypothesis, then show that he can have complete confidence in a special truth-detecting mental ability that God has given him. Briefly, here are the steps that he goes through.

            The first step is to deduce some details about exactly what kind of thing he is. He still can’t say that he has a body, since at this stage the possibility still remains that the evil genius is deceiving him about the three-dimensional world. However, in the very act of grasping his existence, he is exercising several mental abilities, which he describes here:


But what then am I? A thing which thinks. What is a thing which thinks? It is a thing which doubts, understands, conceives, affirms, denies, wills, refuses, which also imagines and feels. Certainly it is no small matter if all these things pertain to my nature. But why should they not so pertain? Am I not that being who now doubts nearly everything, who nevertheless understands certain things, who affirms that one only is true, who denies all the others, who desires to know more, is averse from being deceived, who imagines many things, sometimes indeed despite his will, and who perceives many likewise, as by the intervention of the bodily organs? [Meditations 2]


Thus, he concludes that he is primarily a thing that thinks, and this includes the mental acts of doubting, understanding, conceiving, affirming, denying, willing, refusing, imagining, and feeling.

            The second step is to prove God’s existence. Medieval philosophers offered a wealth of arguments for God, but most of these assumed that the three-dimensional world exists and, again, Descartes is not yet in a position to assume this. All that he knows for sure so far is his own existence and the kind of mental abilities that he has. However, he devises a different strategy for proving God that doesn’t require believing in the three-dimensional world. As he surveys the contents of his mind, he finds the usual collection of ideas, such as those of trees, animals, buildings. All of these are finite in nature, and are not particularly reliable.  But then he sees within his mind a concept of “infinite perfection”—an idea infinite complexity and goodness. It’s like a gleaming diamond sitting among a pile of dirty rocks. How did that idea get there? He couldn’t have created it himself, he argues, since his limited mental abilities would be incapable of inventing an idea that is so infinitely elaborate. The only possible explanation is that the idea of infinite perfection was implanted in his mind by God himself, who is infinitely perfect. God, then, must exists. Once he knows that God exists, he proceeds to the third step, which is to debunk the evil genius hypothesis. His argument here is straightforward: God could not be a deceiver since deception is an imperfection, and God is infinite perfection.

            The fourth step is to prove that he can have confidence in a special truth-detecting mental ability that God has given him. According to Descartes, whenever we encounter obvious truths such as 2+2=4, something like a light bulb goes off in our heads to alert us that we’re on the right track. This “light of nature,” as he calls, it involves clarity and distinctness: we see clearly and distinctly that 2+2=4. The key question is whether Descartes can trust this truth-detecting light bulb as an accurate indicator of truth. If there’s an evil genius, then it’s not reliable, since the evil genius might be hot wiring it to go off at the wrong time. However, having proven that God is not a deceiver, Descartes can have full confidence that God created him with a reliable clarity and distinctness mechanism. The end result is that every time Descartes examines a new truth and the light goes on, he can add this to his ever-growing edifice of secure knowledge. Armed with the truth-detecting mechanism of clarity and distinctness, Descartes goes on to prove the existence of the three-dimensional world. That is, he perceives clearly and distinctly that his normal perceptions of rocks and trees are caused by actual three-dimensional external objects, rather than the result of his imagination or a hallucination.


Spirit-Body Dualism

Once Descartes knows that a three-dimensional physical world exists, he continues by arguing that human beings are constructed of both a physical body and a spirit-mind—a position called spirit-body dualism. Philosophers since ancient times, such as Plato and Plotinus, advocated spirit-body dualism, and, so, as a general theory, Descartes is suggesting nothing new. What is unique to Descartes’ position, though, is how he defends this theory, as we see here:


I concluded that I was a substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent on any material thing. Thus the “I” (that is to say, the mind by which I am what I am) is wholly dis­tinct from the body. It is even more easily known than the [body], and is such that even if the [body] did not exist, [my mind] would still continue to be all that it is. [Discourse on the Method]


His point is that he can conceive of himself existing as a thinking thing, even if he had no body and there was no three-dimensional world—sort of like if he was just a spirit-mind bobbing around in the spirit realm. Thinking, he concludes, is an exclusive attribute of a non-physical spirit entity. Non-three-dimensional spirit things think, and three-dimensional physical things do not think. While we do have physical bodies, our thinking does not occur in our bodies, but only in the spirit part of us.

            Thus, according to Descartes, I am composed of a spirit-mind that thinks, and a physical body that is essentially an unconscious machine. However, the two interact with each other. When my physical body picks up sensory information, such as a bee landing on my arm, this data mechanically flows through my nerves, into my brain, and ultimately is detected by my conscious spirit. Also, when I think of performing some bodily movement, such as swatting the bee off my arm, the thought within my spirit-mind triggers a physical reaction in my brain that mechanically causes my hand to move.

            Where precisely in my brain does data transfer back and forth between my physical body and spirit-mind? According to Descartes, it occurs in the pineal gland. All the wiring in my brain, he argues, feeds to that single point right in the center of my brain:


It is merely the most inward of all its parts, namely, a certain very small gland which is situated in the middle of its substance and so suspended above the duct whereby the animal spirits in its anterior cavities have communication with those in the posterior. It is such that the slightest movements which take place in it may alter very greatly the course of these spirits. And, reciprocally, the smallest changes which occur in the course of the spirits may do much to change the movements of this gland. [The Passions of the Soul, 1:31]


The pineal gland, then, is the master switchboard that conveys information back and forth between my physical body and spirit-mind. From Descartes’ perspective, it seemed reasonable to hypothesize that the pineal gland performed this task since it is so conveniently situated in the middle of the brain. However, we now know that the pineal gland does not serve this function, and, in fact, no part of the brain mediates the flow of all conscious mental activity. Explaining precisely how spirit-minds and physical bodies interact with each other is a serious challenge for spirit-body dualists, and several rationalist philosophers after Descartes offered their own solutions, as we will see.



Descartes was so influential that after his death many philosophers and scientists adopted and refined his basic views. Among these “Cartesians”, as they were called, was French philosopher Nicholas Malebranche (1638–1715), who was especially interested in solving the problem of how physical bodies and spirit-minds interact. Son of a royal secretary, Malebranche was born in Paris with a malformed spine, which caused him pain throughout his life. He was kept home until age 16, later studied at the Sorbonne in Paris, and was ordained into the Catholic church at around age 25. Around the same time he first became acquainted with a work by Descartes, which upon reading gave him heart palpitations and forced him to set it aside for a bit. In his mid-30s he composed his most famous work, The Search After Truth (1674-75), which aimed to combine key elements of Augustine’s and Descartes’ philosophy. Gaining prominence through a succession of publications, he became embroiled in a bitter dispute with a famous critic over some of the more controversial aspects of his views. This ultimately led to his Search being placed on the index of prohibited books. Nevertheless, he continued writing and revising his Search up to his death at age 77.

            Much of Malebranche’s philosophy is driven by the problem with spirit-body dualism noted above. The central issue is that our minds are non-three-dimensional spirit, and our bodies are three-dimensional matter; it is an exceedingly difficult task to move information from one realm to the other. Descartes believed that his pineal gland theory solved the problem. Malebranche, though, offers a radically different solution: God performs the task by shuttling information back and forth between our spirit-minds and physical bodies. His theory comes in two parts: God giving our minds sensory information, and God initiating bodily movement.


Sensory Information: Viewing through God

Consider first the problem of how sensory information gets from my physical body into my spirit-mind. Again, imagine that a bee lands on my arm; somehow that sensory information moves from my arm, to my brain, and then jumps into my spirit-mind in the non-physical realm. In fact, according to Malebranche, it requires a virtual miracle to jump realms. All the sensory information in my body and brain is three-dimensional; for me to perceive it in my non-physical spirit-mind, it must get converted into a non-three-dimensional form. He explains the difficulty of this conversion process here, speculating about what it would take to turn a physical stone into a non-physical angel:


It is even more difficult to produce an angel [that is made of spirit] out of a [physical] stone, than to produce the angel out of nothing. This is because to make an angel out of a stone (so far as it can be done) the stone must be annihilated, and afterwards the angel created. But simply to create an angel, nothing is to be annihilated. If therefore the mind produces its ideas from the material impressions which the brain receives from objects, it must always do the same thing, or a thing as difficult, or even more difficult than if it created them. Since ideas are spiritual, they cannot be produced of material images, which have no proportion with them. [Search After Truth, 3.2.3]


Thus, the gulf between physical sensory information in our bodies and conscious experience of that information in our spirit-minds is so enormous, that only God can convert the one to the other.

            How exactly does God convert information in our physical bodies to our spirit-minds? There are two steps to this divine process. First, God has within his own mind a master database of all possible perceptions that anyone in the world will ever experience, and all of this data is in non-three-dimensional form. For example, within this database there is the complete range of perceptual experiences that someone might have of Paris in the year 1700, or in the year 2000, or for that matter in the year 3000. It contains the complete range of perceptual experiences of city parks, underground caves, music concerts, prison cells, basements, closets, you name it: God has stored the perceptual information of all of those experiences. Second, at the appropriate time, God feeds the appropriate spirit-mental images into our spirit-minds. For example, if a bee is landing on my physical arm right now, God will inject into my spirit-mind the appropriate visual and tactile sensation of the bee. Malebranche describes this process here:


It is absolutely necessary that God should have in himself the ideas of all the beings he has created, since otherwise he could not have produced them. And, thus, he sees all those beings by considering the perfections which he includes in himself, and to which all beings are related. Moreover, it is necessary to know that God is very strictly united to our souls by his presence, so that we may say that he is the location of spirits, just as space is the location of bodies. These two things being supposed, it is certain that the mind may see what there is in God, which represents created beings, since that is very spiritual, very intelligible, and most present to the mind. Thus the mind may see in God the works of God, supposing God be willing to disclose to our minds what there is in God which represents those works. [Search after Truth, 3.2.6]


According to the above, for God to have created everything in the world, he needed to first have a complete understanding of those things—when a specific tree will grow on a given plot of land, when someone will chop it down, and when someone will carve it into a wooden chair. All of this information is stored in God’s database of possible perceptions. Not only does God use this as a blueprint for creating the world, he also feeds information from this database into our spirit-minds when the time is just right.


Bodily Movement: God causing all Physical Motion

The second part of Malebranche’s theory involves how God gets data from our minds in the spirit realm and converts that into motion in our physical bodies. Again, suppose that I want to get the bee off my arm by swatting it with my hand. My spirit-mind issues a command, for example, “raise my right hand”; God then detects this command in my mind, and activates a sequence of movements in my physical body, such as chemical activity in my brain and nerves, which lead to muscle contractions in my right hand. He writes,


It appears most certain to me that the will of spirits is not capable of moving the smallest body in the world. For it is evident there is no necessary connection between the will we have of moving our arms, and the motion of them. It is true, they are moved when we please, and by that means we are the natural cause of their motion. But natural causes are not true causes; they are only occasional ones, which act merely through the power and efficacy of God, as I have already explained. [Search after Truth, 6.2.3]


God, then, is the true cause of the motion in our bodies, while the physical activity itself is just the occasional or incidental cause. Accordingly, this aspect of Malebranche’s theory is called “occasionalism.”

            Thus, God plays a decisive role in reading my thoughts and triggering the appropriate physical activity in my brain. However, according to Malebranche, God’s role in causal activity goes far beyond this. Every causal movement in the physical world is activated by God; we can call this stronger view “extreme occasionalism.” The simple reason for this more extreme view is that, according to Malebranche, all physical things are inert and completely incapable of moving themselves: “It is evident that all bodies, both great and small, have no power of moving themselves: a mountain, a house, a stone, a grain of sand” (ibid, 6.2.3). An infinite spirit, on the other hand, is capable of moving itself. Thus, if a physical thing is in motion, the cause of its motion must be some spirit which has that power—and God is the only spirit that does have it. He writes,


We have only two sorts of ideas, that of bodies, and that of spirits. Since we ought to speak only of those things which we conceive, we should reason according to these two ideas. Since therefore the idea we have of all bodies shows us that they cannot move themselves, it must be concluded that they are moved by spirits only. But when we examine the idea we have of all finite minds, we do not see the necessary connection between their wills and the motion of any body whatever it may be. On the contrary, we see that there is none, nor can there be any. From this we ought to conclude (if we will argue according to our knowledge) that as no body is able to move itself, so there is no created spirit that can be the true or principal cause of the motion of any body whatever. [Ibid]


More formally, the argument that Malebranche offers is this:


1. Only physical bodies and spirits exist.

2. Physical bodies cannot causally move things themselves.

3. Therefore, only spirits can causally move things.

4. Finite spirit-minds cannot causally move things.

5. God, who is infinitely perfect, can causally move things.

6. Therefore, only God can causally move things.


Thus, for whatever motion takes place in the world, God is the only being with the power to produce it and, accordingly, he is the true active cause of all motion, in spite of how things might initially appear.


God and Evil

A final influential component of Malebranche’s philosophy is his explanation of the problem of evil, that is, why an all good God would create a world with such imperfection and suffering. The world as it currently stands is far from perfect, and its imperfections have resulted in untold human misery. The suffering that we experience has two main sources: human-made causes and natural causes. According to Malebranche human-made suffering, such as crime and war, is solely the result of human free choice, and we have no one to blame for that but ourselves. He writes,


[God has not made] the disorder which has crept into it through the bad use we make of our freedom, for God has made no infidels. He only permits men to search after him. I understand this, though I do not know the reason for it. [Dialogues on Metaphysics and Religion, 9.9]


The more serious problem concerns the naturally caused suffering that we experience, such as natural disasters, diseases, and physical deformities. This is solely the work of God and seems inconsistent with his goodness. How can we explain why God “who today covers the whole country with flowers and fruit, will ravage it tomorrow with frost and hail?” (ibid).

            Malebranche’s answer is that naturally caused suffering is a byproduct of God’s efforts to create the most perfect world, using the fewest number of general laws required. There are two parts to his point. First, God’s attribute of wisdom inclines him to act in the most efficient way possible: “he cannot act uselessly” (ibid, 10). Given the kind of being God is, God has no choice but to act efficiently; thus, his guiding rule when creating things is to act with the greatest amount of simplicity and fruitfulness. To that end, God has fashioned a specific number of general laws of nature, which guide all natural events. Except for the occasional miracle that overrides the general laws, God sticks to this plan. The second part of Malebranche’s point is that the natural world, as it currently is, strikes the right balance between the simplicity of its general laws and the perfection in its operations. Sure, God could have made the natural world with fewer defects, but that would have required adding more and more natural laws, thus diminishing its simplicity:


If the defects of the universe, wherein we dwell, diminish this relation, the simplicity, fruitfulness and wisdom of its ways and laws which God follows increase it all the more. A world more perfect, but produced in ways less fruitful and less simple, would not bear to the same extent as ours the character of the divine attributes. This is why the world is full of infidels, monstrosities, disorder of all kinds. [Ibid, 9.11]


Thus, according to Malebranche, we must recognize that no one but God is responsible for the imperfections in the natural world that result in human suffering. At the same time, though, we must recognize that, even with its imperfections, the current world best reflects God’s grandeur insofar as it reflects God’s need to design things in the most efficient way. 



Another philosopher strongly influenced by Descartes is Baruch Spinoza (1632–1677). Born in Amsterdam of Portuguese Jewish parents, Spinoza was raised in the orthodox faith which included intense study of the Jewish Talmud. By the young age of 24, his critical nature came into conflict with Jewish beliefs. Unable to stop his expounding on these, and fearful that it would compound the fact that the Jews were not considered Amsterdam citizens at that time, the Synagogue authorities took the ultimate step and issued a condemnation of him such that his teaching should not be listened to, and no one was to be in contact with him. Ironically, at this point, he adapted the Latin form of his first name, Benedictus, meaning blessed. His parents having both died, Spinoza passed on his share of the family fortune to his brother and stepsister, refused prestigious teaching positions and  developed a career as a lens-grinder, making quality optical and magnifying lenses. For additional income, he sold stolen jewelry smuggled into Holland from France. After becoming entrenched in philosophy, Spinoza’s goal was to establish a clandestine philosophical sect and change the world. On publishing the Theologico-Politcal Treatise anonymously and finding it badly received, he was unable to publish any more of his works, but continued to write nonetheless. In time, inhaling glass dust from lens grinding led to a lung illness and ultimately his death. After this, by Spinoza’s own instructions, his friends collected his writings, edited them secretly, and quietly submitted them for publication, all the while cautious lest they be confiscated and destroyed. The plan succeeded, and the most important of these works is his Ethics, which he completed two years before his death.

            The full title of Spinoza’s Ethics is “Ethics Demonstrated in a Geometrical Manner,” which signals from the start that the work’s methodology and writing style are unconventional. Spinoza believed that geometry offered the best approach to systematically proving things, insofar as it begins with basic definitions and axioms, then deduces more complex propositions from these. This is precisely the system that he uses in his Ethics, which on the whole makes the work feel more like a mathematics text than a philosophical treatise. Beneath the mathematical exterior, though, is an innovative theory about God, the cosmos, and human nature.


God as Nature: Substance Monism

In a nutshell, Spinoza holds the pantheistic view that God is identical to nature as a whole, and human beings are just little pieces of God. While pantheism is a hallmark of Eastern philosophy, it is a view of God that has largely been rejected by Western philosophers, two notable exceptions being the ancient Greek philosophers Parmenides and Plotinus. The traditional monotheistic conception of God is that he is an all powerful being that created the universe, but stands apart from everything he creates: the universe is not a piece of God himself. This traditional monotheistic position—sometimes called the transcendent view of God—is completely at odds with the pantheistic position that the entire universe is God. This is what Spinoza holds, and it is this aspect of his philosophy that got him into so much trouble with his Jewish community. To understand God, according to Spinoza, we must look to nature itself and attempt to understand it. The first philosophical task that he sets out for himself in the Ethics is to prove the pantheistic position that God is the totality of the natural world, or, using his terminology, “Besides God, no substance can be granted or conceived” (Ethics, 1.14). The specific argument that he offers for his position is this:


1. There cannot exist in the universe two or more substances having the same nature or attribute. (Proposition 5)

2. God (defined as a substance consisting of infinite attributes, of which each expresses eternal and infinite essentiality) necessarily exists. (Proposition 11)

3. Therefore, besides God, no substance can be granted or conceived. (Proposition 14)


Even for experienced philosophers the above argument is a challenge to grasp, but its key point is in the first premise: two substances cannot share the same attribute. That is, whatever attributes might exist, each one can only belong to one thing at a time. As an analogy, consider that the quality of being “The President of the United States” can only belong to one person at a time, and cannot be shared by two people. So too with the major attributes that we find in nature: they can only belong to one thing at a time. Premise 2 tells us that, by definition, God’s nature consists of every major attribute, and thus there are no such attributes left for other possible things. Since a thing can't exist if it doesn't have any attributes, then God is the only thing that exists. The upshot of the above argument, then, is that nothing in the universe exists apart from God, and everything that we see in the natural world is indeed part of God. Thus Spinoza writes “God is one, that is, only one substance can be granted in the universe, and that substance is absolutely infinite” (ibid, 1.14). The specific pantheistic position he is advocating here is sometimes called “substance monism”—that is, there is only one substance that exists.

            Once proving that God is identical to nature as a whole, the next step is to explain precisely what God’s features consist of. Traditional monotheists would say that God’s principal attributes are supreme power, supreme knowledge and supreme goodness. Spinoza, though, does not go this route. First, according to Spinoza, God has an infinite number of major attributes, but humans can only conceive of two: consciousness and three-dimensionality. That is, God has a huge spirit-soul and a huge physical body, which are superimposed on each other. Second, God’s attributes take on different mini-features—or “modes” as he calls them—such as the forms of rocks, trees, and people. These things are all just special arrangements of three-dimensional stuff within God, or, in the case of humans, three-dimensional stuff plus consciousness. To help illustrate the distinction within God between major attributes and mini-features (“modes”), let’s consider the main attributes and mini-features of a green candy gummy bear. It has two major attributes: it is made of gooey stuff that gives it shape, and it is green, which gives it color. Aside from these two major attributes, it has several mini-features. Most noticeably, some of the gooey stuff is in the shape of a nose, or an ear, or an arm, or a leg. Think, then, of God and the universe as though it was a giant green gummy bear. It has two major attributes: greenness (consciousness) and gooey stuff (three-dimensionality). Further, it has several mini-features, such as an ear or a nose (rocks, trees, people), which are different arrangements of the two major attributes of greenness and gooey stuff (consciousness and three-dimensionality). Thus, everything that we see in the natural world is some type of mini-feature of God—me, you, the Empire State Building, Mount Everest. For Spinoza, “Whatsoever is, is in God, and without God nothing can be, or be conceived” (ibid, 1.15).

            Spinoza’s view of God’s two major attributes provides a convenient solution to the spirit-body problem initially raised by Descartes. Recall again the central problem: our minds are non-three-dimensional spirit, and our bodies are three-dimensional matter; it requires a virtual miracle to move information from one realm to the other. Spinoza’s solution is a theory that today we call parallelism: consciousness and three-dimensionality are part of the same divine substance, so spirit-minds and physical bodies automatically operate in parallel with each other. He writes,


Whatsoever can be perceived by the infinite intellect as constituting the essence of substance, belongs altogether only to one substance: consequently, substance thinking and substance extended are one and the same substance, comprehended now through one attribute, now through the other. So also, a mode of extension and the idea of that mode are one and the same thing, though expressed in two ways. [Ibid, 2.7]


Human beings are mini-features of God, and exemplify God’s two attributes of consciousness and three-dimensionality. As little pieces of God, our minds and bodies perform in perfect synchronization with each other, just as God’s major attributes of consciousness and three-dimensionality are perfectly coordinated with each other. So, when a bee lands on my arm and initiates a flow of sensory data in my three-dimensional body, my conscious mind automatically perceives the bee. My mind and my body are thus automatically synchronized, since God’s major attributes of consciousness and three-dimensionality are already synchronized:


Mind and body are one and the same thing, conceived first under the attribute of thought, secondly, under the attribute of extension. Thus it follows that the order or series of things is identical, whether nature be conceived under the one attribute or the other; consequently the order of states of activity and passivity in our body is simultaneous in nature with the order of states of activity and passivity in the mind. [Ibid, 3.2]


The information doesn’t need to jump from the physical realm to the spirit realm, as Descartes supposed. Rather, my body and mind are operating on parallel paths that are unified in God’s single substance.


Determinism and Human Bondage

At first glance we might think that Spinoza’s view of “God” is just a pantheistic version of the Judeo-Christian-Muslim God who answers our prayers and watches over us. Not so. His view of “God” is quite non-personal, and does not include anything more than what he takes to be the totality of the natural world. God is best approached through science and philosophy, not through religious worship and prayer. In fact, he uses the terms “God” and “nature” interchangeably. His naturalistic view of God-as-nature is most clearly seen in his position that God is completely determined—with no free will—and does not act with any purpose. This is precisely what we’d expect a scientist to say about the natural world. The universe has no free will, and everything within the universe happens mechanically; God-as-nature has no plan for our lives or the world in which we live. God does not watch over us, communicate with us, intervene on our behalf, or bend natural events based on our prayers. The mechanistic order of the universe is all that there is:


There is no need to show at length that nature has no particular goal in view, and that final causes are mere human figments. This, I think, is already evident enough . . . [from the fact] that everything in nature proceeds from a sort of necessity, and with the utmost perfection. [ibid, Appendix]


The reason why we erroneously think that God acts with a purpose is that we improperly impose willful purposes on natural events outside of us. The wind blows a tree over on my crazy neighbor’s house, and I think that God is punishing him. My farm fields have a good growing season, and I think that God has answered my prayers and is rewarding me. Since I cannot guide nature myself, I wrongly conclude that God willfully guides natural events for my benefit.

            What about human beings: do we have free wills even if God doesn’t? No, Spinoza argues. Since humans are just little pieces of God-as-nature, our actions are also completely determined: “Nothing in nature is contingent, but all things are determined to exist and operate in a particular manner by the necessity of the divine nature” (ibid, 1:29). Again, we erroneously believe that we have free wills, even when the truth is that we don’t. The source of this erroneous belief, according to Spinoza, is that we are conscious only of the fact that we perform actions, but are completely unaware of our actions’ true underlying causes buried deep within our mental construction. I am conscious of the fact that I reach out and pick up an apple, but I have no consciousness at all of the mental machinery that went into me performing that action. I then mistake the consciousness of my action with free will, and thus wrongly assume that I picked up the apple from my own free will. He writes, “experience teaches us no less clearly than reason, that men believe themselves to be free, simply because they are conscious of their actions, and unconscious of the causes whereby those actions are determined” (ibid, 3.2). Spinoza gives several examples of humans who, in special circumstances, clearly lack free will, yet still believe they act freely:


Thus an infant believes that of its own free will it desires milk, an angry child believes that it freely desires vengeance, a timid child believes that it freely desires to run away. Further, a drunken man believes that he utters from the free decision of his mind words which, when he is sober, he would willingly have withheld. Thus, too, a delirious man, a talkative woman, a child, and others of like complexion, believe that they speak from the free decision of their mind, when they are in reality unable to restrain their impulse to talk. [Ethics, 3.2]


In each of the above cases, a person believes he is freely performing an action, yet from an impartial perspective we can see that the action is determined by purely mechanical psychological factors. Spinoza argues that if a falling stone had consciousness, it might similarly say that it’s falling from its own free will (“Letter to G.H. Schuller”). All of our actions, then, are completely determined, in spite of how it seems to us individually from our own perspectives.

            For Spinoza, there is a sinister implication to the fact that human actions are determined by underlying psychological causes: our emotions can easily take control of our lives and force us to do things that go against good judgment. We have a fundamental human frailty that makes it difficult for us to restrain our emotions; he calls this frailty “bondage” since “when a man is a prey to his emotions, he is not his own master, but lies at the mercy of fortune: so much so, that he is often compelled, while seeing that which is better for him, to follow that which is worse” (ibid, 4, Preface). For this reason, people are more easily swayed by emotional appeals than by true reason, and even genuine knowledge itself has the negative effect of stirring up conflicts within our minds that lead to every kind of emotion. Thus if we have any hope of acting reasonably, “it is necessary to know the power and the infirmity of our nature, before we can determine what reason can do in restraining the emotions, and what is beyond her power” (ibid, 4.17). Spinoza is not saying that we can freely choose to restrain our emotions if we try hard enough. Rather, he says, if we understand how emotions take control of us, that knowledge itself might help mechanically alter our psychological framework and thus change how we perform our actions. Our actions will always be determined, and we will always be inclined to act emotionally. But the more knowledge that we have about our emotions, the more that this knowledge will automatically induce us to act more rationally.


Free Speech

Spinoza was a major advocate of free speech, and he had personal reasons for being so. Well aware of the controversial nature of his pantheistic view of God-as-nature, he knew that his views could be published during his life only if there was a political climate of tolerance towards free speech. He thus composed his Theologico-Politcal Treatise, containing perhaps the staunchest defense of free speech in its day, hoping it would help foster an environment of toleration. His general position is that governments should permit people to freely express their opinions, so long as those opinions do not lead to subversive and harmful actions. In fact, he argues, a society is more likely to rebel when its government restricts people to holding only a narrow and irrational set of beliefs.

            He makes six specific claims in defense of free speech. First, he argues, it “it is impossible to deprive men of the liberty of saying what they think” (Theologico-Politcal Treatise, 20.71). We have both the power and natural right to be master of our own thoughts, and, try as we might, it is nearly impossible for us to stay silent on issues that concern us. Thus, the contents of our minds—our reasons and judgments—cannot be placed under the control of someone else. This freedom extends to speaking our minds, and not merely silently reflecting on controversial ideas within the privacy of our own heads. Even issues as touchy as proper and improper worship of God fall within the bounds of our liberty of expression. Second, free speech can be granted for everyone without injuring governmental authority, so long as people don’t act contrary to the existing laws. Spinoza recognizes that governmental authority is critical to maintaining a peaceful society, and we should not act in ways that undermine that authority. However, he argues, free expression does not undermine the government’s ability to keep law and order.

            Third, free speech can be exercised without disrupting public peace, and any minor inconvenience that it creates can easily be remedied. Similar to the previous point, Spinoza concedes that, in the interests of social peace, we must give up our right to act as we choose. However, there is no benefit to social peace by giving up free expression. Fourth, people can exercise free speech without compromising their loyalty to the government. There is a fear that if people are allowed to speak their minds, then they would quickly become vocal critics of the government, and worse yet, express outright disloyalty. Spinoza contends that this worry is unrealistic. Fifth, laws are entirely useless when they aim to restrict the expression of purely speculative ideas. Those who love truth, virtue, and knowledge would simply break those laws while giving preference to their higher ideals. Finally, free speech is in fact necessary for the preservation of public peace, since death in the name of freedom is considered a glory:


when people try to take it away, and bring to trial, not only the acts which alone are capable of offending, but also the opinions of mankind, they only succeed in surrounding their victims with an appearance of martyrdom, and raise feelings of pity and revenge rather than of terror. [ibid, 20.77]


The job of rulers, then, should be confined to controlling how people behave, and not extend to what people think or say.



The final major thinker in the continental rationalist tradition was German philosopher Gottfried Willhelm Leibniz (1646–1716). Born in Leipzig, Leibniz was entrenched in study at quite a young age, possibly intensified at age 6 by the death of his father--a professor of philosophy at the University of Leibzig--who inspired a love of learning and left a massive library, which became accessible to the young boy the next year. In the next few years, Leibniz taught himself Latin and Greek. By the time he entered the University of Leibzig at age 14, he had also mastered philosophy, theology and law. At the age of 20, he graduated with degrees in law and philosophy. Ironically, the University considered his shortfall to be mathematics, although he later developed calculus. When the University would not assure him a position teaching law after graduation, Leibniz took his thesis and submitted it to the University of Altdorf instead. In five months time, he had his doctorate in law. His first job was as an alchemist, a subject he knew nothing about. He spent most of the rest of his life working for two notable German families, mainly as a political diplomat. A charming and well-mannered man, Leibniz had friends and admirers throughout Europe, maintaining correspondence with more than 600 people. But Leibniz’s reputation was in decline in his last couple of years with disputes about his claim to inventing calculus independent of Newton. When he died at age 70, none of his fellow political diplomats attended his funeral. By the time of his death, he had just one book-length publication, The Theodicy, but shortly thereafter a steady stream of his unpublished letters and documents had made their way into print, finally giving him the reputation that he deserved.


Monads in an Infinitely Divisible Plenum

We’ve seen that one of the characteristics of rationalistic philosophy is the use of deductive arguments that are modeled after mathematical proofs. While Leibniz did not push this approach to the extreme that Spinoza did, he still shared Descartes’ drive for certainty. Leibniz writes, “Although I am one of those who have done much work on mathematics, I have constantly meditated on philosophy from my youth up, for it has always seemed to me that in philosophy there was a way of establishing something solid by means of clear proofs” (New System). Another distinguishing feature of rationalist philosophers during the 17th century is that they constructed elaborate metaphysical systems in their efforts to solve longstanding philosophical puzzles. Leibniz has the most elaborate of these. However, underlying its intricacy, his philosophical system is driven by one key assumption: God maximizes his creative abilities. Everything God performs as creator is done in the most perfect, desirable, unified, and orderly way possible. This is evident in creation’s ultra-high level of structural complexity and also in its perfect goodness. He writes,


God who possesses supreme and infinite wisdom acts in the most perfect manner not only metaphysically, but also from the moral standpoint. And with respect to ourselves it can be said that the more we are enlightened and informed in regard to the works of God the more will we be disposed to find them excellent and conforming entirely to that which we might desire. [Discourse, 1]


Sometimes when God maximizes his creative abilities, he opts for the most complex arrangement of things, which allows him to actualize his creative powers most fully. And, since God is infinitely powerful, he opts to create the most infinitely complex world that he can. In some sense, then, God does not follow Ockham’s razor and its principle of simplicity, which would constrain his activities. In fact, in some cases God follows a principle that is the exact opposite of Ockham’s razor.

            In developing his system, Leibniz returns to a pair of issues that preoccupied ancient Greek philosophers 2000 years earlier: whether there is any vacuum of empty space, and whether matter is infinitely divisible. Atomists argued that there is indeed empty space, and matter is not infinitely divisible. The tiniest particles of matter – atoms – cannot be divided into anything smaller, and they exist within a vacuum of empty space. By contrast, Anaxagoras took the opposite position on both issues. First, Anaxagoras held that there is no vacuum of empty space, and thus all area within the cosmos is packed full of material stuff. That is, there is a plenum—the contrary of a vacuum. Second, all material stuff within the plenum is infinitely divisible: it can be divided in half again and again, on to infinity. Leibniz sides with Anaxagoras on both issues: the universe is an infinitely divisible plenum. Leibniz’s main argument in defense of the plenum is based on the view that God maximizes his creative abilities: the more matter there is in the universe, the better this reflects God’s creativity:


I lay it down as a principle, that every perfection which God could impart to things without derogating from their other perfections, has actually been imparted to them. Now let us fancy a space wholly empty. God could have placed some matter in it, without derogating in any respect from all other things. Therefore he has actually placed some matter in that space. Therefore, there is no space wholly empty. Therefore all is full. [Fourth Letter to Clarke]


The same rationale applies to particles of matter: the more the better; and in fact, the very best scenario would be a universe filled with an infinite number of infinitely small substances that are incapable of being divided at all. He writes, “each portion of matter is not only infinitely divisible, as the ancients recognized, but is also actually subdivided without limit, each part into further parts” (Monadology, 65). These infinitely tiny, indivisible substances he calls monads

            Leibniz’ view of monads faces an immediate obstacle: if monads themselves are infinitely tiny and each one takes up no space, how can they jointly unite to make a three-dimensional chunk of matter? Leibniz’s answer is that monads are sort of like mathematical points. Suppose that I hold an apple in my hand; within that spherical area there are an infinite number of mathematical points. While each point itself is infinitely small and does not itself take up any space, all combined they account for the complete spherical area of the apple. While monads are not exactly the same thing as mathematical points, they are what he calls metaphysical points, and can be understood in a similar way. Each monad is a non-three-dimensional spirit-like substance, which, like mathematical points, have infinitely tiny exactness within a three-dimensional area. Unlike mathematical points, however, monads are real things and have actual substance:


Physical points are indivisible in appearance only: mathematical points are exact, but they are nothing but modalities. It is only metaphysical points, or points of substance (constituted by forms or souls), which are both exact and real; and without them there would be nothing real, since without true unities there would be no plurality. [The New System]


Leibniz draws on another conception from ancient Greek philosophy to help explain how monads—as metaphysical points—have a reality. They are, he says, “substantial forms.” That is, they are realities like Plato’s forms that have a spirit-like existence, yet are not composed of three-dimensional material stuff. However, three-dimensional material things, like an apple, emerge from the collective unity of the monads within a given area of space.


Perception, Appetite, and Mirroring in Monads

Granted, then, that the three-dimensional world of material stuff is composed of infinitely tiny monads. How do monads form things? Leibniz’s answer is that monads have four special internal abilities that enable them to congeal together and take on the shape of rocks, trees, people, and everything else that we see. Those three abilities are perception, appetite, and mirroring. Consider first the ability of perception: monads have the ability to perceive what other monads are doing around them. It’s not a conscious perception, such was when I or my cat are aware of a tree limb falling in the yard. Instead, it’s more like how an electronic motion detector might sense things around it without having the ability to mentally reflect on it. He calls this minimal sensory capacity “minute perception,” and notes that animals have this as well: “We might perhaps add that brutes have perception, and that it is not necessary that they should have thought, that is to say, should have reflection or anything that can be the object of reflection” (New Essays, 2.9).

            The second ability of monads is appetite. When perceiving what other monads are like around them, they form a desire to change and shape themselves to fit into the crowd. For example, if one monad perceives that those around it are taking on the form of a rock, it will then assume that appearance as well. The monad’s ability to transform itself in many ways resembles what biologists now tell us about how stem cells work in humans and animals. When stem cells are placed next to, say, a kidney, they sense their new location and transform into a kidney cell, thus becoming part of the kidney.

            The third ability of monads is to mirror the entire universe. Each monad has embedded within it the master plan of everything that takes place in the universe. The source of this master plan is the intimate connection that each monad has to those surrounding them; as every monad is surrounded on all sides by other monads, there is a direct connection between monads from one end of the universe to the other. He writes,


Because the world is a plenum, everything is connected and each body acts upon every other body, more or less according to the distance, and by reaction is itself affected thereby; it follows that each monad is a mirror, living or endowed with internal activity, representative according to its point of view of the universe, and as regulated as the universe itself. [“Principles of Nature and Grace,” 3]


To borrow another analogy from contemporary biology, it is as though each monad contains the DNA instructions for the layout of the entire universe.

            Thus, through perception, appetite, and mirroring, each monad knows where it is, what its neighbors are doing, and what it should do in order to realize the master plan of the universe. And, as the events in the universe change, the monads themselves will undergo the appropriate change in appearance to bring this about.


Dominant Monad Souls and Parallalism

According to Leibniz, the monads that form living things like plants and animals operate slightly differently than those that form non-living things like rocks. At the heart of all living things, he argues, is a dominant monad soul that rules over surrounding monads and unifies them a localized organic structure. He writes,


It is evident, then, that every living body has a dominating entelechy, which in animals is the soul. The parts, however, of this living body are full of other living beings, plants and animals, which, in turn, have each one its entelechy or dominating soul. [“Monadology,” 70]


For example, at the very center of an apple is a dominant monad that signals to surrounding ones that they must take the shape of an apple. Thus, by unifying together surrounding monads, it transforms them into one machine and directs their operations. As time progresses and the apple slowly rots, each monad making up the apple will be going through a change in appetite, thereby progressively displaying a rotten appearance. When we move on to animals, there is a dominant monad which can do more than simply perceive: it has sentience, which means that it can feel, be aware of things, and have memory. This monad is the animal’s soul.

            Moving on further to human beings, as with animals, the dominant monad within me arranges the rest of the monads within me to form my body, and it gives me sentience. Added to this, though, the dominant monad in me contains the added ability to reason; this gives me my mind, or “rational soul.” Like Descartes and the other rationalists, Leibniz is a spirit-body dualist: human beings are composed of both a physical body and a non-physical soul. For Leibniz, my nonphysical soul is the dominant monad within me that gives me sentience and rationality; my physical body, by contrast, is composed of non-dominant monads, which band together under the direction of my dominant monad soul. As a spirit-body dualist, Leibniz faces the same problem as did the other rationalists. That is, since our minds are non-three-dimensional spirit, and our bodies are three-dimensional matter, how does sensory information move back and forth between the spirit and physical realms? Leibniz solves the problem with his own unique version of parallelism.

            As we’ve seen with Spinoza, parallelism is the theory that a person’s physical body and spirit-mind exist in completely separate realms, but events in each realm magically unfold in perfect synchronization with each other; thus, there is no need for my physical body and spirit-mind to directly communicate and interact with each other. In Spinoza’s case, the two realms are synchronized since they are both part of God’s pantheistic identity. Leibniz is no pantheist, though, and his rationale is different: the mind-spirit and body operate in perfect synchronization like two clocks that are in perfect agreement; they are both part of God’s perfect master plan and thus stay in synchronization. He writes,


Imagine two clocks or watches which agree perfectly . . . . [as when we] construct these two clocks with so much art and accuracy as to assure their future agreement. Put now the soul and the body in place of these two clocks; their agreement . . . . [will be best explained by] the way of pre-established harmony. From the beginning God has made each of these two substances of such a nature that merely by following its own peculiar laws, received with its being, it nevertheless accords with the other. It is just as if there were a mutual influence or as if God always put his hand thereto in addition to his general cooperation. [“The New System,” Postscript, 1696]


While it appears that my body and soul are interacting with each other—shuttling sensory information back and forth, they are not. Instead, they are operating in perfect synchronization where “the soul follows its own laws, and the body likewise follows its own laws” (“Monadology,” 78). Suppose that a bee lands on my arm and I swat it away. According to Leibniz, the laws of nature that govern the physical realm bring it about that a physical bee lands on my physical arm, and my physical hand swats it off. At the same time, though, laws governing the spirit-realm bring it about that I mentally perceive the sensation of a bee, and then make a willful decision to swat it off my arm. The laws the two realms and everything that unfolds in each are in perfect synchronization because God has designed the world that way as part of his great master plan – or “pre-established harmony” as Leibniz calls it.


Evil and the Best of All Possible Worlds

The most famous part of Leibniz’s philosophy is that which deals with the problem of evil, that is, the potential conflict between human suffering on the one hand and God’s goodness on the other. Consider, for example, the immeasurable suffering caused by Hitler in his efforts to exterminate the Jews and dominate the world. If God is good, why would he have allowed this to happen? In a nutshell, Leibniz’s solution is that God has created the best possible world, and even the evils that we see are so integrated into God’s larger master plan, that, on balance, they actually contribute to making the world a better place than it would otherwise be.

            The first step in this solution is to show that God creates only the best possible world. Imagine that at the outset of creation God had before him the blueprints of countless possible worlds that he might create. He examines them one at a time to see which is the best and deserving of creating. One possible world, for example, consists of only one brick that floats around in outer space. Another possible world has stars and planets, just like ours, but contains no living things. Yet another is like the previous one but includes plants and animals; however, it contains no human beings. And then there are all the possible worlds that contain humans. In some of these worlds Hitler exists, and in others he doesn’t. God then makes his choice: his wisdom tells him which is the best of these possible worlds, his goodness has him choose it, and his power has him create it. He writes,


Now as there are an infinity of possible universes in the ideas of God, and but only one of them can exist, there must be a sufficient reason for the choice of God which determines him to select one rather than another.

            And this reason is to be found only in the fitness or in the degree of perfection which these worlds possess, each possible thing having the right to claim existence in proportion to the perfection which it involves.

            This is the cause for the existence of the greatest good; namely, that the wisdom of God permits him to know it, his goodness causes him to choose it, and his power enables him to produce it. [“Monadology,” 53-55]


According to the above, each possible world contains a specific degree of perfection, and God simply singles out the one that has the most.

            The second step in Leibniz’s solution is to understand how the evil that exists in this most perfect world is naturally balanced through punishment. Just as there is a pre-existing harmony between realms of the body and soul, there is a similar harmony between the natural world and moral world. Thus, if I commit some evil, I can count on being punished through some natural phenomenon, such as a disease or natural disaster. Similarly, if I perform a good act, I can count on nature rewarding me, such as through good health or good weather. He writes,


We can say also that God, the Architect, satisfies in all respects God the Law Giver, that therefore sins will bring their own penalty with them through the order of nature, and because of the very structure of things, mechanical though it is. And in the same way the good actions will attain their rewards in mechanical way through their relation to bodies, although this cannot and ought not always to take place without delay. [Ibid, 89]


Thus, whenever I experience suffering, my first recourse is to consider whether I’ve committed some evil for which I am being punished.

            The third step in Leibniz solution is to understand how enormous evils, such as those perpetrated by Hitler, are part of God’s master plan in this best of all possible worlds. If God is all powerful, it seems that it was within his ability to create a world without such enormous evils. Leibniz responds with a classic answer given by Augustine and others, that is, sometimes evil is necessary to bring about a greater good:


The best course is not always that one which tends towards avoiding evil, since it is possible that the evil may be accompanied by a greater good. For example, the general of an army will prefer a great victory with a slight wound to a state of affairs without wound and without victory. [Theodicy, Summary]


For example, while the fall of Adam brought about enormous evil, it also had the positive benefit of leading to the incarnation of God through Jesus, which “gave to the universe something nobler than anything there would otherwise have been” (ibid). Further, he argues, a world with free creatures who commit evil is better than a world without free creatures. Human free choice is clearly the ultimate source of all evil and suffering, and it would certainly be within God’s power to intervene to stop the evil. For example, God could have dropped a bolder on Hitler’s head when Hitler decided to give up being an artist and go into politics instead. However, Leibniz argues, there is no moral requirement for God to intervene in such dramatic ways, when he can counterbalance such evil through more natural means:


It was consistent with order and the general good for God to grant to certain of his creatures the opportunity to exercise their freedom, even when he foresaw that they would turn to evil: for God could easily correct the evil, and it was not fitting that in order to prevent sin he should always act in an extraordinary way. [Ibid]


Thus, a world with evil may be better than a world without evil. Ultimately, Leibniz argues, we may never have an entirely satisfying answer since we are unable to comprehend the totality of God’s plan, and, thus, we need to simply trust that this is the best of all possible worlds, in spite of how it might appear to us at the moment.




The Need to Doubt only the Foundations of Knowledge through the Senses

It is now some years since I detected how many were the false beliefs that I had from my earliest youth admitted as true, and how doubtful was everything I had since constructed on this basis. From that time I was convinced that I must once and for all seriously undertake to rid myself of all the opinions which I had formerly accepted, and begin to build anew from the foundation, if I wanted to establish any firm and permanent structure in the sciences. But as this enterprise appeared to be a very great one, I waited until I had attained an age so mature that I could not hope that at any later date I should be better fitted to execute my design. This reason caused me to delay so long that I should feel that I was doing wrong were I to occupy in deliberation the time that yet remains to me for action. Today, then, since very opportunely for the plan I have in view I have delivered my mind from every care [and am happily agitated by no passions] and since I have procured for myself an assured leisure in a peaceable retirement, I will at last seriously and freely address myself to the general upheaval of all my former opinions.

            Now for this object it is not necessary that I should show that all of these are false; I will perhaps never arrive at this end. But reason already persuades me that I ought no less carefully to withhold my assent from matters which are not entirely certain and indubitable than from those which appear to me evidently to be false. Consequently, if I am able to find in each one some reason to doubt, this will suffice to justify my rejecting the whole. For that end it will not be necessary for me to examine each one in particular, which would be an endless task. But because the destruction of the foundations necessarily brings with it the downfall of the rest of the edifice, I will only in the first place attack those principles upon which all my former opinions rested.

            All that up to the present time I have accepted as most true and certain I have learned either from the senses or through the senses; but it is sometimes proved to me that these senses are deceptive, and it is wiser not to trust entirely to anything by which we have once been deceived.


Doubting Hypothesis 1: My Senses are Unreliable (e.g., Optical Illusions)

It may be that the senses sometimes deceive us concerning things which are hardly perceptible, or very far away. However, there are yet many others to be met with as to which we cannot reasonably have any doubt, although we recognize them by their means. For example, there is the fact that I am here, seated by the fire, wearing a dressing gown, having this paper in my hands and other similar matters. How could I deny that these hands and this body are mine? Perhaps only comparing myself to certain people who lack sense, whose cerebella are so troubled and clouded by the violent vapors of black bile, that they constantly assure us that they think they are kings when they are really quite poor, or that they are clothed in purple when they are really without covering, or who imagine that they have a head made of pottery, or are nothing but pumpkins, or are made of glass. But they are mad, and I should not be any the less insane were I to follow examples so extravagant.


Doubting Hypothesis 2: Maybe I am Dreaming

At the same time I must remember that I am a man, and that consequently I am in the habit of sleeping, and in my dreams I represent to myself the same things or sometimes even less probable things, than do those who are insane in their waking moments. How often has it happened to me that in the night I dreamt that I found myself in this particular place, that I was dressed and seated near the fire, while in reality I was lying undressed in bed! At this moment it does indeed seem to me that it is with eyes awake that I am looking at this paper; that this head which I move is not asleep, that it is deliberately and of set purpose that I extend my hand and perceive it; what happens in sleep does not appear so clear nor so distinct as does all this. But in thinking over this I remind myself that on many occasions I have in sleep been deceived by similar illusions, and in dwelling carefully on this reflection I see so evidently that there are no certain indications by which we may clearly distinguish wakefulness from sleep that I am lost in astonishment. My astonishment is such that it is almost capable of persuading me that I now dream.

            Now let us assume that we are asleep and that all these particulars, for example, that we open our eyes, shake our head, extend our hands, and so on, are but false delusions. Let us also reflect that possibly neither our hands nor our whole body are such as they appear to us to be. At the same time we must at least confess that the things which are represented to us in sleep are like painted representations which can only have been formed as the counterparts of something real and true. In this way, those general things at least (that is, eyes, a head, hands, and a whole body) are not imaginary things, but things really existent. For, as a matter of fact, painters, even when they study with the greatest skill to represent sirens and satyrs by forms the most strange and extraordinary, cannot give them natures which are entirely new, but merely make a certain medley of the members of different animals. Or if their imagination is extravagant enough to invent something so novel that nothing similar has ever before been seen, and that then their work represents a thing purely fictitious and absolutely false, it is certain all the same that the colors of which this is composed are necessarily real. For the same reason, although these general things—that is, [a body], eyes, a head, hands, and such like—may be imaginary, we are bound at the same time to confess that there are at least some other objects yet more simple and more universal, which are real and true. Of these, just in the same way as with certain real colors, all these images of things which dwell in our thoughts, whether true and real or false and fantastic, are formed.

            To such a class of things pertains corporeal nature in general, and its extension, the figure of extended things, their quantity or magnitude and number, as also the place in which they are, the time which measures their duration, and so on.

            That is possibly why our reasoning is not unjust when we conclude from this that Physics, Astronomy, Medicine and all other sciences which have as their end the consideration of composite things, are very dubious and uncertain; but that Arithmetic, Geometry and other sciences of that kind which only treat of things that are very simple and very general, without taking great trouble to determine whether they are actually existent or not, contain some measure of certainty and an element of the indubitable. For whether I am awake or asleep, two and three together always form five, and the square can never have more than four sides, and it does not seem possible that truths so clear and apparent can be suspected of any falsity [or uncertainty].


Doubting Hypothesis 3: Maybe an Evil Genius Deceives me

Nevertheless I have long had fixed in my mind the belief that an all-powerful God existed by whom I have been created such as I am. But how do I know that he has not brought it to pass that there is no earth, no heaven, no extended body, no magnitude, no place, and that nevertheless [I possess the perceptions of all these things and that] they seem to me to exist just exactly as I now see them? And, besides, as I sometimes imagine that others deceive themselves in the things which they think they know best, how do I know that I am not deceived every time that I add two and three, or count the sides of a square, or judge of things yet simpler, if anything simpler can be imagined? But possibly God has not desired that I should be thus deceived, for he is said to be supremely good. If, however, it is contrary to his goodness to have made me such that I constantly deceive myself, it would also appear to be contrary to his goodness to permit me to be sometimes deceived, and nevertheless I cannot doubt that he does permit this. . . .

            I will then suppose, not that God who is supremely good and the fountain of truth, but some evil genius not less powerful than deceitful, has employed his whole energies in deceiving me. I will consider that the heavens, the earth, colors, figures, sound, and all other external things are nothing but the illusions and dreams of which this genius has availed himself in order to lay traps for my gullibility. I will consider myself as having no hands, no eyes, no flesh, no blood, nor any senses, yet falsely believing myself to possess all these things. I will remain obstinately attached to this idea, and if by this means it is not in my power to arrive at the knowledge of any truth, I may at least do what is in my power [that is, suspend my judgment], and with firm purpose avoid giving credence to any false thing, or being imposed upon by this arch deceiver, however powerful and deceptive he may be. But this task is a laborious one, and insensibly a certain lethargy leads me into the course of my ordinary life. Just as a captive who in sleep enjoys an imaginary liberty, when he begins to suspect that his liberty is but a dream, fears to awaken, and conspires with these agreeable illusions that the deception may be prolonged, so insensibly of my own accord I fall back into my former opinions, and I dread awakening from this slumber, lest the laborious wakefulness which would follow the tranquility of this calmness should have to be spent not in daylight, but in the excessive darkness of the difficulties which have just been discussed.


Review: Extent of Doubt so Far

The Meditation of yesterday filled my mind with so many doubts that it is no longer in my power to forget them, yet I do not see in what manner I can resolve them. Just as if I had all of a sudden fallen into very deep water, I am so baffled that I can neither make certain of setting my feet on the bottom, nor can I swim and so support myself on the surface. I will nevertheless make an effort and follow anew the same path as that on which I yesterday entered, that is, I will proceed by setting aside all that in which the least doubt could be supposed to exist, just as if I had discovered that it was absolutely false. I will ever follow in this road until I have met with something which is certain, or at least, if I can do nothing else, until I have learned for certain that there is nothing in the world that is certain. Archimedes, in order that he might draw the terrestrial globe out of its place, and transport it elsewhere, demanded only that one point should be fixed and immovable. In the same way I will have the right to conceive high hopes if I am happy enough to discover one thing only which is certain and indubitable.

            I suppose, then, that all the things that I see are false; I persuade myself that nothing has ever existed of all that my fallacious memory represents to me. I consider that I possess no senses; I imagine that body, figure, extension, movement and place are but the fictions of my mind. What, then, can be distinguished as true? Perhaps nothing at all, unless that there is nothing in the world that is certain.


I Still Know that I Exist (I Think, Therefore I am)

But how can I know there is not something different from those things that I have just considered, of which one cannot have the slightest doubt? Is there not some God, or some other being by whatever name we call it, who puts these reflections into my mind? That is not necessary, for is it not possible that I am capable of producing them myself? I myself, am I not at least something? But I have already denied that I had senses and body. Yet I hesitate, for what follows from that? Am I so dependent on body and senses that I cannot exist without these? But I was persuaded that there was nothing in all the world, that there was no heaven, no earth, that there were no minds, nor any bodies: was I not then likewise persuaded that I did not exist? Not at all; of a surety I myself did exist since I persuaded myself of something [or merely because I thought of something]. But there is some deceiver or other, very powerful and very cunning, whoever employs his ingenuity in deceiving me. Then without doubt I exist also if he deceives me, and let him deceive me as much as he will, he can never cause me to be nothing so long as I think that I am something. So that after having reflected well and carefully examined all things, we must come to the definite conclusion that this proposition: I am, I exist, is necessarily true each time that I pronounce it, or that I mentally conceive it.




All opinions [about God freely directing events] arise from commonly held notion that all things in nature act as men themselves act, namely, with an end in view. It is accepted as certain, that God himself directs all things to a definite goal (for it is said that God made all things for humans, and humans that he might worship him). I will, therefore, consider this opinion, asking first, why it obtains general acceptance, and why all men are naturally so prone to adopt it. Secondly, I will point out its falsity. Lastly, I will show how it has given rise to prejudices about good and bad, right and wrong, praise and blame, order and confusion, beauty and ugliness, and the like.


People Think that God acts Purposefully since they wrongly assume that People act Purposefully with Free Will

However, this is not the place to deduce these misconceptions from the nature of the human mind. It will be sufficient here, if I assume as a starting point, what ought to be universally admitted, namely, that all people are born ignorant of the causes of things, that all have the desire to seek for what is useful to them, and that they are conscious of such desire. From here it follows, first, that people think themselves free inasmuch as they are conscious of their volitions and desires, and never even dream, in their ignorance, of the causes which have disposed them so to wish and desire. Secondly, that people do all things for an end, namely, for that which is useful to them, and which they seek.

            Thus it happens that they only look for a knowledge of the final causes of events, and when these are learned, they are content, as having no cause for further doubt. If they cannot learn such causes from external sources, they are compelled to turn to considering themselves, and reflecting what end would have induced them personally to bring about the given event, and thus they necessarily judge other natures by their own. Further, as they find in themselves and outside themselves many means which assist them not a little in their search for what is useful, for instance, eyes for seeing, teeth for chewing, herbs and animals for yielding food, the sun for giving light, the sea for breeding fish, etc., they come to look on the whole of nature as a means for obtaining such conveniences. Now as they are aware that they found these conveniences and did not make them, they think they have cause for believing, that some other being has made them for their use. As they look upon things as means, they cannot believe them to be self-created. But, judging from the means which they are accustomed to prepare for themselves, they are bound to believe in some ruler or rulers of the universe endowed with human freedom, who have arranged and adapted everything for human use.

            They are bound to estimate the nature of such rulers (having no information on the subject) in accordance with their own nature, and therefore they assert that the gods ordained everything for the use of humans, in order to bind humans to themselves and obtain from him the highest honor. Hence also it follows that everyone thought out for himself, according to his abilities, a different way of worshipping God, so that God might love him more than his fellows, and direct the whole course of nature for the satisfaction of his blind greed and insatiable avarice. Thus the prejudice developed into superstition, and took deep root in the human mind; and for this reason everyone strove most zealously to understand and explain the final causes of things; but in their attempt to show that nature does nothing in vain, nothing which is useless to humans, they only seem to have demonstrated that nature, the gods, and men are all mad together. Consider, I ask you, the result: among the many helps of nature they were bound to find some hindrances, such as storms, earthquakes, diseases, etc., so they declared that such things happen, because the gods are angry at some wrong done them by men, or at some fault committed in their worship. Day by day, experience protested and showed by infinite examples that good and evil fortunes fall to the circumstance of pious and impious alike. Still they would not abandon their inveterate prejudice, for it was more easy for them to class such contradictions among other unknown things of whose use they were ignorant, and thus to retain their actual and innate condition of ignorance, than to destroy the whole fabric of their reasoning and start afresh.

            They therefore laid down as an axiom, that God's judgments far transcend human understanding. Such a doctrine might well have sufficed to conceal the truth from the human race for all eternity, if mathematics had not furnished another standard of truth in considering solely the essence and properties of figures without regard to their final causes. There are other reasons (which I need not mention here) besides mathematics, which might have caused men's minds to be directed to these general prejudices, and have led them to the knowledge of the truth.


God does not Act from a Purpose

I have now sufficiently explained my first point. There is no need to show at length that nature has no particular goal in view, and that final causes are mere human figments. This, I think, is already evident enough, both from the causes and foundations on which I have shown such prejudice to be based, and also from Prop. 16., and the Corollary of Prop. 32, and, in fact, all those propositions in which I have shown, that everything in nature proceeds from a sort of necessity, and with the utmost perfection. However, I will add a few remarks, in order to overthrow this doctrine of a final cause utterly. That which is really a cause it considers as an effect, and vice versa: it makes that which is by nature first to be last, and that which is highest and most perfect to be most imperfect. Passing over the questions of cause and priority as self-evident, it is plain from Props. 21, 22, and 23 that that effect is most perfect which is produced immediately by God. The effect which requires for its production several intermediate causes is, in that respect, more imperfect. But if [to the contrary] those things which were made immediately by God were made to enable him to attain his end, then the things which come after, for the sake of which the first were made, are necessarily the most excellent of all.

            Further, this doctrine does away with the perfection of God: for, if God acts for an object, he necessarily desires something which he lacks. Certainly, theologians and metaphysicians draw a distinction between the object of want and the object of assimilation. Still they confess that God made all things for the sake of himself, not for the sake of creation. They are unable to point to anything prior to creation, except God himself, as an object for which God should act, and are therefore driven to admit (as they clearly must), that God lacked those things for whose attainment he created means, and further that he desired them.

            We must not omit to notice that the followers of this doctrine, anxious to display their talent in assigning final causes, have imported a new method of argument in proof of their theory – namely, a reduction, not to the impossible, but to ignorance; thus showing that they have no other method of exhibiting their doctrine. For example, if a stone falls from a roof onto someone's head, and kills him, they will demonstrate by their new method, that the stone fell in order to kill the man. For, if it had not by God's will fallen with that object, how could so many circumstances (and there are often many concurrent circumstances) have all happened together by chance? Perhaps you will answer that the event is clue to the facts that the wind was blowing, and the man was walking that way. "But why," they will insist, "was the wind blowing, and why was the man at that very time walking that way?" If you again answer, that the wind had then sprung up because the sea had begun to be agitated the day before, the weather being previously calm, and that the man had been invited by a friend, they will again insist: "But why was the sea agitated, and man invited at that time?" So they will pursue their questions from cause to cause, till at last you take refuge in the will of God – in other words, the sanctuary of ignorance. So, again, when they survey the frame of the human body, they are amazed; and being ignorant of the causes of so great a work of art, conclude that it has been fashioned, not mechanically, but by divine and supernatural skill, and has been so put together that one part will not hurt another.

            Hence anyone who seeks for the true causes of miracles, and strives to understand natural phenomena as an intelligent being, and not to gaze at them like a fool, is set down and denounced as an impious heretic by those, whom the masses adore as the interpreters of nature and the gods. Such persons know that, with the removal of ignorance, the wonder which forms their only available means for proving and preserving their authority would vanish also. But I now quit this subject, and pass on to my third point.




Please answer all of the following questions.


1. What are Descartes four rules of inquiry and his four provisionary codes of morals?

2. What are Descartes’ three reasons for doubting the reliability of the senses?

3. What, according to Descartes, are the features of his true identity, and what is his proof for God’s existence?

4. Why, according to Descartes, is God not a deceiver, and what is the function of the clarity and distinctness mechanism?

5. What is Descartes’ explanation for how sensory information in my physical body interacts with my conscious non-physical spirit-mind?

6. Explain Malebranche’s theory of seeing all things in God.

7. Explain Malebranche’s theories of mind-body occasionalism and extreme occasionalism.

8. What is Malebranche’s solution to the problem of evil, particularly regarding suffering caused through nature?

9. Explain Spinoza’s views of God is the only substance, and mind-body parallelism.

10. Explain Spinoza’s view that God has no freewill and does not act with a purpose.

11. Explain Spinoza’s views of determinism, and human bondage.

12. What is Spinoza’s general view on the subject of free speech?

13. Explain Leibniz’s view of monads.

14. Explain Leibniz’s theory of mind-body parallelism.

15. What is Leibniz solution to the problem of evil?

[Reading 1: Descartes on Doubt and Certainty]

16. What are the things that Descartes doubts because of the dream hypothesis?

17. What are the things that Descartes doubts because of the Evil Genius hypothesis?

18. What is Descartes’ Archimedes analogy, and his point when he says “I think, therefore I am”?

[Reading 2: Spinoza on God not Willfully Directing the Course of Nature]

19. According to Spinoza, how did ignorant people come up with the idea that God acts with a purpose?

20. What is Spinoza’s argument for why God does not act for a purpose?

[Question for Analysis]

21. Pick any one of the following views by a rationalist philosopher and criticize it in a minimum of 150 words. Descartes: four rules of inquiry; evil genius hypothesis; I think therefore I am; proof of God’s existence; proof of the external world; pineal gland theory. Malebranche: seeing all things through God; mind-body occasionalism; extreme occasionalism; why God permits evil. Spinoza: God as the only substance; mind-body parallelism; God does not act with a purpose; determinism; human bondage. Leibniz: monads; mind-body parallelism; the best of all possible worlds.