Why is descartes considered the founder of modern rationalism

This means that existence is contained in the essence of an infinite substance, and therefore God must exist by his very nature. Indeed, any attempt to conceive of God as not existing would be like trying to conceive of a mountain without a valley — it just cannot be done.

Recall that in the First Meditation Descartes supposed that an evil demon was deceiving him. So as long as this supposition remains in place, there is no hope of gaining any absolutely certain knowledge. The next step is to demonstrate that God cannot be a deceiver. But, since God has all perfections and no imperfections, it follows that God cannot be a deceiver.

For to conceive of God with the will to deceive would be to conceive him to be both having no imperfections and having one imperfection, which is impossible; it would be like trying to conceive of a mountain without a valley. It is absolutely certain because both conclusions namely that God exists and that God cannot be a deceiver have themselves been demonstrated from immediately grasped and absolutely certain intuitive truths.

This means that God cannot be the cause of human error, since he did not create humans with a faculty for generating them, nor could God create some being, like an evil demon, who is bent on deception.

Rather, humans are the cause of their own errors when they do not use their faculty of judgment correctly. So God would be a deceiver, if there were a clear and distinct idea that was false, since the mind cannot help but believe them to be true. Hence, clear and distinct ideas must be true on pain of contradiction. So if one affirms that an idea corresponds to a thing itself when it really does not, then an error has occurred. This faculty of judging is described in more detail in the Fourth Meditation.

Here judgment is described as a faculty of the mind resulting from the interaction of the faculties of intellect and will. Here Descartes observes that the intellect is finite in that humans do not know everything, and so their understanding of things is limited. But the will or faculty of choice is seemingly infinite in that it can be applied to just about anything whatsoever.

The finitude of the intellect along with this seeming infinitude of the will is the source of human error. For errors arise when the will exceeds the understanding such that something laying beyond the limits of the understanding is voluntarily affirmed or denied. To put it more simply: people make mistakes when they choose to pass judgment on things they do not fully understand. So the will should be restrained within the bounds of what the mind understands in order to avoid error.

If one only makes judgments about what is clearly and distinctly understood and abstains from making judgments about things that are not, then error would be avoided altogether.

In fact, it would be impossible to go wrong if this rule were unwaveringly followed. Descartes explains it best at Principles , part 1, section Here he first states that it is a distinction between two or more substances. Second, a real distinction is perceived when one substance can be clearly and distinctly understood without the other and vice versa. Third, this clear and distinct understanding shows that God can bring about anything understood in this way.

Hence, in arguing for the real distinction between mind and body, Descartes is arguing that 1 the mind is a substance, 2 it can be clearly and distinctly understood without any other substance, including bodies, and 3 that God could create a mental substance all by itself without any other created substance.

So Descartes is ultimately arguing for the possibility of minds or souls existing without bodies. Descartes argues that mind and body are really distinct in two places in the Sixth Meditation. The first argument is that he has a clear and distinct understanding of the mind as a thinking, non-extended thing and of the body as an extended, non-thinking thing.

So these respective ideas are clearly and distinctly understood to be opposite from one another and, therefore, each can be understood all by itself without the other. Two points should be mentioned here. So the premises of this argument are firmly rooted in his foundation for absolutely certain knowledge. Second, this indicates further that he knows that God can create mind and body in the way that they are being clearly and distinctly understood.

Therefore, the mind can exist without the body and vice versa. From this it follows that mind and body cannot have the same nature, for if this were true, then the same thing would be both divisible and not divisible, which is impossible. Hence, mind and body must have two completely different natures in order for each to be able to be understood all by itself without the other.

Although Descartes does not make the further inference here to the conclusion that mind and body are two really distinct substances, it nevertheless follows from their respective abilities to be clearly and distinctly understood without each other that God could create one without the other.

The crux of the difficulty lies in the claim that the respective natures of mind and body are completely different and, in some way, opposite from one another.

On this account, the mind is an entirely immaterial thing without any extension in it whatsoever; and, conversely, the body is an entirely material thing without any thinking in it at all. This also means that each substance can have only its kind of modes.

For instance, the mind can only have modes of understanding, will and, in some sense, sensation, while the body can only have modes of size, shape, motion, and quantity. But bodies cannot have modes of understanding or willing, since these are not ways of being extended; and minds cannot have modes of shape or motion, since these are not ways of thinking.

The difficulty arises when it is noticed that sometimes the will moves the body, for example, the intention to ask a question in class causes the raising of your arm, and certain motions in the body cause the mind to have sensations.

But how can two substances with completely different natures causally interact? Pierre Gassendi in the Fifth Objections and Princess Elizabeth in her correspondence with Descartes both noted this problem and explained it in terms of contact and motion. The main thrust of their concern is that the mind must be able to come into contact with the body in order to cause it to move. Yet contact must occur between two or more surfaces, and, since having a surface is a mode of extension, minds cannot have surfaces.

Therefore, minds cannot come into contact with bodies in order to cause some of their limbs to move.

Furthermore, although Gassendi and Elizabeth were concerned with how a mental substance can cause motion in a bodily substance, a similar problem can be found going the other way: how can the motion of particles in the eye, for example, traveling through the optic nerve to the brain cause visual sensations in the mind, if no contact or transfer of motion is possible between the two?

This could be a serious problem for Descartes, because the actual existence of modes of sensation and voluntary bodily movement indicates that mind and body do causally interact. But the completely different natures of mind and body seem to preclude the possibility of this interaction. Hence, if this problem cannot be resolved, then it could be used to imply that mind and body are not completely different but they must have something in common in order to facilitate this interaction.

Therefore, Descartes could not really come to a clear and distinct understanding of mind and body independently of one another, because the nature of the mind would have to include extension or body in it. Descartes, however, never seemed very concerned about this problem. The reason for this lack of concern is his conviction expressed to both Gassendi and Elizabeth that the problem rests upon a misunderstanding about the union between mind and body.

Though he does not elaborate to Gassendi, Descartes does provide some insight in a 21 May letter to Elizabeth. In that letter, Descartes distinguishes between various primitive notions.

The first is the notion of the body, which entails the notions of shape and motion. The second is the notion of the mind or soul, which includes the perceptions of the intellect and the inclinations of the will. The notions entailed by or included in the primitive notions of body and soul just are the notions of their respective modes. This suggests that the notions depending on the primitive notion of the union of soul and body are the modes of the entity resulting from this union.

This would also mean that a human being is one thing instead of two things that causally interact through contact and motion as Elizabeth and Gassendi supposed. Instead, a human being, that is, a soul united with a body, would be a whole that is more than the sum of its parts. Accordingly, the mind or soul is a part with its own capacity for modes of intellect and will; the body is a part with its own capacity for modes of size, shape, motion and quantity; and the union of mind and body or human being, has a capacity for its own set of modes over and above the capacities possessed by the parts alone.

On this account, modes of voluntary bodily movement would not be modes of the body alone resulting from its mechanistic causal interaction with a mental substance, but rather they would be modes of the whole human being. The explanation of, for example, raising the arm would be found in a principle of choice internal to human nature and similarly sensations would be modes of the whole human being.

Hence, the human being would be causing itself to move and would have sensations and, therefore, the problem of causal interaction between mind and body is avoided altogether. However, a final point should be made before closing this section. The position sketched in the previous couple of paragraphs is not the prevalent view among scholars and requires more justification than can be provided here. In the Sixth Meditation , Descartes recognizes that sensation is a passive faculty that receives sensory ideas from something else.

According to the Causal Adequacy Principle of the Third Meditation , this cause must have at least as much reality either formally or eminently as is contained objectively in the produced sensory idea. It, therefore, must be either Descartes himself, a body or extended thing that actually has what is contained objectively in the sensory idea, or God or some creature more noble than a body, who would possess that reality eminently.

It cannot be Descartes, since he has no control over these ideas. It cannot be God or some other creature more noble than a body, for if this were so, then God would be a deceiver, because the very strong inclination to believe that bodies are the cause of sensory ideas would then be wrong; and if it is wrong, there is no faculty that could discover the error.

Accordingly, God would be the source of the mistake and not human beings, which means that he would be a deceiver. So bodies must be the cause of the ideas of them, and therefore bodies exist externally to the mind.

In part II of the Principles , Descartes argues that the entire physical universe is corporeal substance indefinitely extended in length, breadth, and depth. This means that the extension constituting bodies and the extension constituting the space in which those bodies are said to be located are the same.

Here Descartes is rejecting the claim held by some that bodies have something over and above extension as part of their nature, namely impenetrability, while space is just penetrable extension in which impenetrable bodies are located.

Therefore, body and space have the same extension in that body is not impenetrable extension and space penetrable extension, but rather there is only one kind of extension.

Descartes maintains further that extension entails impenetrability, and hence there is only impenetrable extension. Hence, it is not that bodies are in space but that the extended universe is composed of a plurality or plenum of impenetrable bodies. Rather, another body takes the place of the first such that a new part of extension now constitutes that place or space. Here an example should prove helpful. Consider the example of a full wine bottle.

The wine is said to occupy that place within the bottle. Once the wine is finished, this place is now constituted by the quantity of air now occupying it. Notice that the extension of the wine and that of the air are two different sets of bodies, and so the place inside the wine bottle was constituted by two different pieces of extension. Therefore, so long as bodies of the same shape, size and position continue to replace each other, it is considered one and the same place.

This assimilation of a place or space with the body constituting it gives rise to an interesting philosophical problem. A return to the wine bottle example will help to illustrate this point. Recall that first the extension of the wine constituted the place inside the bottle and then, after the wine was finished, that place inside the body was constituted by the extension of the air now occupying it.

It is difficult to see how Descartes would address this issue. This is because an empty space, according to Descartes, would just be a non-extended space, which is impossible. A return to the wine bottle will further illustrate this point. Notice that the place inside the wine bottle was first constituted by the wine and then by air. These are two different kinds of extended things, but they are extended things nonetheless.

Accordingly, the place inside the bottle is constituted first by one body the wine and then by another air. So, under these circumstances, no mode of distance could exist inside the bottle.

Therefore, an empty space cannot exist between two or more bodies. This asymmetry is found in the claim that particular minds are substances for Descartes but not particular bodies.

Rather, these considerations indicate to some that only the whole, physical universe is a substance, while particular bodies, for example, the wine bottle, are modes of that substance. Though the textual issues are many, the main philosophical problem stems from the rejection of the vacuum. The argument goes like this: particular bodies are not really distinct substances, because two or more particular bodies cannot be clearly and distinctly understood with an empty space between them; that is, they are not separable from each other, even by the power of God.

Hence, particular bodies are not substances, and therefore they must be modes. However, this line of reasoning is a result of misunderstanding the criterion for a real distinction. Instead of trying to understand two bodies with an empty space between them, one body should be understood all by itself so that God could have created a world with that body, for example, the wine bottle, as its only existent. But, suffice it to say that the textual evidence is also in favor of the claim that Descartes, despite the unforeseen problem about surfaces, maintained that particular bodies are substances.

The most telling piece of textual evidence is found in a letter to Gibeuf:. From the simple fact that I consider two halves of a part of matter, however small it may be, as two complete substances. I conclude with certainty that they are really divisible. These considerations in general, and this quotation in particular, lead to another distinct feature of Cartesian body, namely that extension is infinitely divisible.

The point is that no matter how small a piece of matter, it can always be divided in half, and then each half can itself be divided in half, and so on to infinity.

These considerations about the vacuum and the infinite divisibility of extension amount to a rejection of atomism. Atomism is a school of thought going back to the ancients, which received a revival in the 17th century most notably in the philosophy and science of Pierre Gassendi.

This mechanistic physics is also a point of fundamental difference between the Cartesian and Scholastic-Aristotelian schools of thought. For the latter as Descartes understood them , the regular behavior of inanimate bodies was explained by certain ends towards which those bodies strive. Furthermore, Descartes maintained that the geometric method should also be applied to physics so that results are deduced from the clear and distinct perceptions of the geometrical or quantifiable properties found in bodies, that is, size, shape, motion, determination or direction , quantity, and so forth.

From what has already been said we have established that all the bodies in the universe are composed of one and the same matter, which is divisible into indefinitely many parts, and is in fact divided into a large number of parts which move in different directions and have a sort of circular motion; moreover, the same quantity of motion is always preserved in the universe.

Since the matter constituting the physical universe and its divisibility were previously discussed, a brief explanation of the circular motion of bodies and the preservation of motion is in order. This principle indicates that something will remain in a given state as long as it is not being affected by some external cause. So a body moving at a certain speed will continue to move at that speed indefinitely unless something comes along to change it.

The second thesis about the circular motion of bodies is discussed at Principles , part II, section This claim is based on the earlier thesis that the physical universe is a plenum of contiguous bodies. On this account, one moving body must collide with and replace another body, which, in turn, is set in motion and collides with another body, replacing it and so on. But, at the end of this series of collisions and replacements, the last body moved must then collide with and replace the first body in the sequence.

This is known as a Cartesian vortex. The principle expressed here is that any body considered all by itself tends to move in a straight line unless it collides with another body, which deflects it. Notice that this is a thesis about any body left all by itself, and so only lone bodies will continue to move in a straight line. However, since the physical world is a plenum, bodies are not all by themselves but constantly colliding with one another, which gives rise to Cartesian vortices as explained above.

The third general law of motion, in turn, governs the collision and deflection of bodies in motion. But if the body collides with a weaker body, then the first body loses a quantity of motion equal to that given in the second. Notice that all three of these principles doe not employ the goals or purposes that is, final causes utilized in Scholastic-Aristotelian physics as Descartes understood it but only the most general laws of the mechanisms of bodies by means of their contact and motion.

In part five of the Discourse on Method , Descartes examines the nature of animals and how they are to be distinguished from human beings. Here Descartes argues that if a machine were made with the outward appearance of some animal lacking reason, like a monkey, it would be indistinguishable from a real specimen of that animal found in nature. But if such a machine of a human being were made, it would be readily distinguishable from a real human being due to its inability to use language.

Hence, it follows that no animal has an immaterial mind or soul. For Descartes this also means that animals do not, strictly speaking, have sensations like hunger, thirst and pain. Rather, squeals of pain, for instance, are mere mechanical reactions to external stimuli without any sensation of pain.

In other words, hitting a dog with a stick, for example, is a kind of input and the squeal that follows would be merely output, but the dog did not feel anything at all and could not feel pain unless it was endowed with a mind. Humans, however, are endowed with minds or rational souls, and therefore they can use language and feel sensations like hunger, thirst, and pain.

The point is that just as the workings of a clock can be best understood by means of the configuration and motion of its parts so also with animal and human bodies.

He then goes on to describe in some detail the motion of the blood through the heart in order to explain that when the heart hardens it is not contracting but really swelling in such a way as to allow more blood into a given cavity. Although this account goes contrary to the more correct observation made by William Harvey, an Englishman who published a book on the circulation of the blood in , Descartes argues that his explanation has the force of geometrical demonstration.

He is famous for having made an important connection between geometry and algebra, which allowed for the solving of geometrical problems by way of algebraic equations.

He was the first major figure in the philosophical movement known as rationalism, a method of understanding the world based on the use of reason as the means to attain knowledge. Modern philosophers have often concerned themselves with the question of dualism. Who is first philosopher in the world? Thales of Miletus. Who are the modern thinkers?

Rationalists Christian Wolff. Baruch Spinoza. Gottfried Leibniz. Who is father of philosophy? What is the concept of modern philosophy? Modern philosophy is the period of philosophy ranging from the 17th century to the 20th century. Who is the greatest modern philosopher? Who is the greatest philosopher in the world? Here are 10 Greatest Philosophers who ever lived Aristotle.

The list of the greatest philosophers is incomplete without Aristotle. Immanuel Kant. What is the most famous work of each philosophers? What is Descartes first principle?

Where do our ideas come from Descartes vs Locke? Why does Locke disagree with Descartes? What is the conclusion of the wax argument?

Back To Top.