René Descartes


“If a man will begin with certainties, he shall end in doubts, but if he will be content to begin with doubts, he shall end in certainties,” says Francis Bacon and thus begins Modern Philosophy. Given the background of centuries of dogmatic scholastic philosophy of saints, it is not surprising that the philosophers decided to take a fresh start and use the shovel of doubt to clear off the debris from the building site. Descartes[1] was among the first to build a new philosophical system from scratch and is rightly known as the father of modern philosophy. Although he has not managed to completely emancipate himself from the scholastic philosophy, he shows a new freshness and innovativeness in his thought, which was carried on by his successors.

Descartes was a French philosopher, scientist and mathematician. He was deeply impressed by mathematics, and is well known for his systematization of analytic geometry. The fact that mathematical method of reasoning gives absolute certainty influenced him greatly, and he sought to give philosophy the same certainty as mathematics. He argued that we should turn to mathematical reasoning as a model for progress in human knowledge. Descartes and his followers believed in deduction, the principle which presupposes some self-evident premises and then draws conclusions from them.

Descartes begins with the principle that only the indubitable is to be accepted and whatever is doubtful must be rejected. He mistrusts everything that he knows—literally, everything. Not only the information given by the senses, his age-old beliefs, his moral values but also things like logic and mathematics. But what is the basis for this doubt? Consider perceptual illusion; a traveller in desert sees a mirage and thinks it is water. Madmen have hallucinations and imagine things that do not exist. Is it not possible that what we perceive is also an illusion? But perceptual illusion can’t be extended to all the empirical knowledge we have. Descartes then examines the dream problem: While we dream, we feel as if we are in the real world. Perhaps, I am in a dream at this very moment. What if this whole of external world is nothing but my dream? Hence, we can doubt the existence of the whole of external reality. What about mathematics and logic? Surely they give us the absolute certainty we need. Descartes goes to the extreme of mistrust and asks his readers to imagine an omnipotent, evil god, who tempers with their minds and causes them to believe in irrational arguments, making them appear rational. [e.g. suppose that 2+2 is not equal to 4, but the deceiving god forces my reason to believe so.] Therefore, even the validity of mathematics cannot survive this dissolvant skepticism. Such a method of doubt is known as ‘Cartesian doubt’ (or Hyperbolic doubt).

This is where we are at the moment: we distrust what our senses tell us, we consider the world to be a mere dream and we suppose a malevolent god who deviates our reason from arriving at true conclusions. Since everything can be doubted, does it mean that we can be certain of nothing?

No, it doesn’t. There is still one thing which survives this extreme mistrust: my very existence. For if I doubt, then I must think, and if I think I must exist. Even a deceiving god can’t deceive me if I didn’t exist. Even if I am deceived, at least I exist. This Descartes expressed as cogitio ergo sum [I think, therefore I am[2].] No matter what I doubt, I can’t doubt the indubitable fact that I exist. The ancient Greek engineer Archimedes said, 'Give me a fulcrum and a firm point, and I alone can move the earth.' In the same manner, Descartes was searching for one indubitable fact to build his philosophical edifice, and this ‘firm point’ is the cogito.

[This argument by Descartes is not very original. In fact, it appears before in the philosophy of St. Augustine. Augustine writes, 'On none of these points do I fear the arguments of the skeptics of the Academy who say: what if you are deceived? For if I am deceived, I am. For he who does not exist cannot be deceived. And if I am deceived, by this same token I am' (City of God, 11:26). However, this was a very small and unimportant part of the Saint’s philosophy.]

Here we must understand that by ‘I think, therefore I am’ Descartes is not making a miniature deduction[3], which goes from ‘I think’ to ‘I exist’ [although it appears to be so due to the word therefore]. Descartes himself helps clarify this that the cogito is not deduced, but is recognized by a simple and immediate act of mental intuition. For Descartes, the very act of thought implies the existence of the ‘I’ that thinks. It is the intuitive realization of one’s own existence, and an expression of the self-conscious awareness.

The ‘cogito ergo sum’ has been criticized by many later philosophers. In ‘I think, therefore I am’, the word ‘I’ is logically illegitimate. The ultimate premise of Descartes should have been ‘There are thoughts’. When Descartes states, ‘I am a thing that thinks’, he is making an unproved assumption of I existing as a thing. However, cogito is acceptable in the grammatical sense.[4] The use of ‘I’ may be justified for the sake of grammatical convenience, but not in the sense of ‘I’ being a thing.

Cogito is the most impressive part of Descartes’s philosophy and it is surprising to see that from this point onwards Descartes fails to apply the skepticism to his own philosophy which he had applied earlier to the knowledge of the world. Descartes says that when he contemplates the certainty of his existence, he finds this truth clear and distinct. He proposes a general rule: everything he perceives clearly and distinctly is true.

Can anything about the external world also be proven beyond doubt? Descartes says yes, but he needs to prove the existence of God to do so. He puts forward a number of arguments, all of which have been derived from scholastic philosophy. Of these arguments, we shall consider here only one, which is known as the Ontological argument. The argument goes like this:

I have, in my mind, an idea of a supremely perfect being. This being is perfect in all respects. Existence is a perfection, hence this supremely perfect being exist. We can understand it with a help of an analogy. We have an idea of a triangle. This triangle has a necessary characteristic that the sum of its three angles is equal to 180°. We can’t form an idea of a triangle, which doesn’t have this characteristic, just as we can’t have an idea of a circle, which has no circumference. Existence is a characteristic of a supremely perfect being, because if it doesn’t exist, it would be imperfect. Hence, the arguments states, the supremely perfect being must exist if we are to have an idea of it. Because we have an idea of God, therefore, God exists.

This argument has had a very mixed reception by philosophers. An average person considers it as out rightly absurd. However, most philosophers have treated this argument with respect. A logical refutation was given by Bertrand Russell in his theory of descriptions[5]. He says that although ‘exists’ is grammatically a predicate[6], logically it performs a different function. “Horses exist” mean that “There are x’s such that ‘x is a horse’ is true.” In the same way, “Mermaids do not exist” is equal to saying “There are no x’s such that ‘x is a mermaid’ is true.” By saying that horses exist, we do not mean, “Horses have a quality that they exist”. Instead we simply imply that there are objects in this world to which we can apply the summarized description in the word ‘horse’. Seeing ‘existence’ is this manner, the Ontological argument fails.

However, let us continue with Descartes’s philosophy. He says that since God is perfect, and deception is a product of imperfection, it means that God does not deceive us. In fact, Descartes is now confident that God being good and non-deceiving has bestowed on him the intellectual abilities necessary for the apprehension of truth.

Descartes continues that as sense perception is a passive ability [i.e. we do not will ourselves to perceive the external world] and I am naturally designed to believe that the ideas of physical objects produced in me are caused by some external source outside my control, it must mean that these external objects truly exist because God has given us this natural belief, and God doesn’t deceive us. Hence, Descartes has shown that he exists, God exists and the external reality exists.

Descartes proceeds to explain this world. He says that there are two substances [a ‘substance’ is a basic and eternal reality] apart from God, namely matter and mind. Matter is characterized by extension and mind has the attribute of thought. Descartes believes that mind is present only in human being, and all other animals are mere biological machines. The question arises, if a human has both mind and matter, then how do these interact? My mind decides to lift the arm, and the arm lifts; how does this interaction take places? Owing to the sharp distinction and wide gulf between mind and matter, Descartes is a called a dualist and this part of his philosophy is known as dualism. Descartes separated the two so much that it became a problem to explain this mutual influence. He himself was not able to solve it, and gave a tentative explanation of ‘Pineal gland’ as the site where this interaction took place, but this was immediately rejected by his successors.

The philosophers succeeding Descartes were primarily concerned with this problem of mind-matter dualism. These philosophers are known as Cartesians and their philosophy is collectively known as Cartesianism.

One of the most important philosophers of Cartesian tradition was Geulincx (1624-1669), who gave the idea known as theory of ‘two clocks’. Assume that we have two clocks which both keep perfect time: whenever one points to hour, the other will strike. And if we could see only the first one and hear only the second one, it would seem as if the first had caused the second to strike. This is precisely the case with mind and matter. Each is ‘divinely synchronized’ and the actions of mind and matter are merely parallel i.e. they do not affect each but only seem to do so. Our mind thinks to lift the arm, and this mental event is precisely synchronized with the bodily event of lifting of arm, and has not caused it. Since physical laws strictly govern all matter, and there is no freedom, and mind is synchronized with matter, it means that mental series of events is also strictly following these laws and has no free will. Hence, Cartesianism leads to pure determinism[7].

Another important Cartesian philosopher was Malebranche (1638-1715). He believed that mind and matter are causally independent and can’t influence each other. When a change takes place in matter, God produces a parallel effect in mind. Hence, in sense perception, we "see all things in god." And similarly, our wills have no causal influence on the material world, but God provides for the coordination of our volitions with the movement of bodies.

Descartes had considerable influence on subsequent philosophy. In the next chapter we shall deal with Spinoza and see how he handles the Cartesian notion of ‘substance’ and develops a highly interesting and influential philosophy.


[1] pronounced ‘Day-cart’
[2] This is known as Descartes’s cogito.
[3] Deduction always contains two premises and a conclusion. For example,
Socrates is a man
All men are mortal
Therefore, Socrates is mortal.
‘I think therefore I am’ contains only one premise, ‘I think’. Hence it is not a deduction.
[4] Later philosophers have claimed that there is no unified thinking being classified as ‘I’ but rather it is a series of individual mental events. In ‘I think’ “I seems to be only a string of events… and [think] really covers complicated relations between events. … It is the particular events which are certain, not the ‘I think’ which Descartes made the basis of his philosophy.” [Outline of Philosophy, by Bertrand Russell. Page 192-193]
[5] See the chapter on Logical Analysis and Russell for details
[6] Predicate is that part of a proposition that is affirmed or denied about the subject. For example, in the proposition: We are mortal, mortal is the predicate. [Excerpted from The American Heritage Dictionary of the English Language, Third Edition Copyright © 1992 by Houghton Mifflin Company.]
[7] That is, our every act is the inevitable effect of a cause, and there is no free will.