Book Summaries Philosophy

Descartes (A History of Western Philosophy)

René Descartes (1596–1650) is rightly considered the founder of modern philosophy. He is the first important philosopher whose outlook is deeply affected by the new physics and astronomy. While he retains much of scholasticism, he does not accept foundations laid by predecessors, but tries to construct a complete and novel philosophic edifice.

This had not happened since Aristotle and is a sign of the new self-confidence that resulted from the progress of science. There is a freshness about his work that is not to be found in any eminent previous philosopher since Plato. All the intermediate philosophers were teachers, with the professional superiority belonging to that avocation. Descartes writes, not as a teacher, but as a discoverer and explorer, anxious to communicate what he has found. His style is easy and unpedantic, addressed to intelligent men of the world rather than to pupils.

Bertrand Russell, A History of Western Philosophy


Descartes worked in short bursts and was not very industrious. He was a philosopher, a mathematician, and a man of science. In philosophy and mathematics, his work was of supreme importance; in science, though creditable, it was not so good as that of some of his contemporaries.

His great contribution to geometry was the invention of co-ordinate geometry.

Descartes’s two most important books in philosophy are the Discourse on Method (1637) and the Meditations (1642). They overlap, and it is not necessary to keep them apart.

In these books Descartes begins by explaining the method of ‘Cartesian doubt’. To have a firm basis for his philosophy, he resolves to make himself doubt everything that he can manage to doubt. As he realized that this will be time consuming, he will act according to conventional rules. This will leave his mind free from dealing with the consequences of his doubts.


His skepticism begins with the senses. Can I doubt, he says, that I am sitting here by the fire in a dressing-gown? Yes, for sometimes I have dreamt that I was here when in fact I was naked in bed. And madmen sometimes hallucinate, so it may be that I am mad.

But dreams give us copies of real things. If you dream of winged horse, it is only because you have seen horses and wings.

Arithmetic and geometry, which are not concerned with particular things, are therefore more certain than physics and astronomy; they are true even of dream objects, which do not differ from real ones as regards number and extension. Even in regard to arithmetic and geometry, however, doubt is possible. It may be that God causes me to make mistakes whenever I try to count the sides of a square or add 2 to 3.

Bertrand Russell, A History of Western Philosophy

If not God, an evil demon might be misleading me.

There remains, however, something that I cannot doubt: no demon, however cunning, could deceive me if I did not exist. I may have no body: this might be an illusion. But thought is different. ‘While I wanted to think everything false, it must necessarily be that I who thought was something; and remarking that this truth, I think, therefore I am, was so solid and so certain that all the most extravagant suppositions of the sceptics were incapable of upsetting it, I judged that I could receive it without scruple as the first principle of the philosophy that I sought.’

Bertrand Russell, A History of Western Philosophy

This passage contains what is most important in the philosophy of Descartes.

Most philosophers since Descartes have attached importance to the theory of knowledge, and their doing so is largely due to him. ‘I think, therefore I am’ makes mind more certain than matter, and my mind (for me) more certain than the minds of others.


Having now secured a firm foundation, Descartes sets to work to rebuild the edifice of knowledge. The I that has been proved to exist has been inferred from the fact that I think, therefore I exist while I think, and only then. If I ceased to think, there would be no evidence of my existence. I am a thing that thinks, a substance of which the whole nature or essence consists in thinking, and which needs no place or material thing for its existence. The soul, therefore, is wholly distinct from the body and easier to know than the body; it would be what it is even if there were no body.

Descartes next asks himself: why is the cogito so evident? He concludes that it is only because it is clear and distinct. He therefore adopts as a general rule the principle: All things that we conceive very clearly and very distinctly are true. He admits, however, that there is sometimes difficulty in knowing which these things are.

Bertrand Russell, A History of Western Philosophy

‘Thinking’ is used by Descartes in a very wide sense. A thing that thinks, he says, is one that doubts, understands, conceives, affirms, denies, wills, imagines, and feels—for feeling, as it occurs in dreams, is a form of thinking. Since thought is the essence of mind, the mind must always think, even during deep sleep. Descartes now resumes the question of our knowledge of bodies.

Bertrand Russell, A History of Western Philosophy

Consider the honeycomb. Some things are apparent to the senses, like the taste of honey. It has a color, shape, size, and texture. Its qualities change if heated. But even if its qualities change, the wax persists. Therefore, what appeared to the senses was not the wax itself.

The wax itself is constituted by extension, flexibility, and motion, which are understood by the mind, not by the
imagination. The thing that is the wax cannot itself be sensible, since it is equally involved in all the appearances of the wax to the various senses. The perception of the wax ‘is not a vision or touch or imagination, but an inspection of the mind’.

You do not see the wax any more than you see men in the street when you see hats and coats. It is your power of judgement that tells you what you saw.

This leads to different ideas. Descartes says that the most common error is to that that your ideas are like outside things. Ideas seem to come in three sorts.

(1) those that are innate, (2) those that are foreign and come from without (3) those that are invented by me.

We are inclined to believe that the second sort of ideas are like outside objects in that they imprint their likeness on me, since they seem to affect our behavior without our consent. But is this correct? Ideas of senses seem to be involuntary, but they could be like dreams which are involuntary and yet come from within. Just because something is involuntary does not necessarily make it an external cause.

Further, you can have two different ideas about the same external object. The sun as it appears to the senses versus the sun that astronomers talk about. They cannot both be like the sun, and it is more likely that the perception of the sun that comes from direct experience is less like the sun than the astronomer’s sun.

But there are still skeptical arguments about the existence of the external world that are yet to be refuted. This can only be done by first proving the existence of God.

Descartes’s proofs of the existence of God are not very original; in the main they come from scholastic philosophy. They were better stated by Leibniz, and I will omit consideration of them until we come to him. When God’s existence has been proved, the rest proceeds easily. Since God is good, He will not act like the deceitful demon whom Descartes has imagined as a ground for doubt. Now God has given me such a strong inclination to believe in bodies that He would be deceitful if there were none; therefore bodies exist. He must, moreover, have given me the faculty of correcting errors. I use this faculty when I employ the principle that what is clear and distinct is true. This enables me to know mathematics, and physics also, if I remember that I must know the truth about bodies by the mind alone, not by mind and body jointly.

Bertrand Russell, A History of Western Philosophy

The constructive part of Descartes’s theory of knowledge is less interesting than the earlier destructive part. It uses many scholastic maxims, such as that an effect can never have more perfection than its cause, which have somehow escaped the initial critical scrutiny. No reason is given for accepting these maxims, although they are certainly less self-evident than one’s own existence, which is proved with a flourish of trumpets.

Bertrand Russell, A History of Western Philosophy

The method of critical doubt was the main contribution Descartes made to philosophy, although he did so half-heartedly. It is clear that it can only be fruitful if skepticism stops somewhere.

If there is to be both logical and empirical knowledge, there must be two kinds of stopping points: indubitable facts, and indubitable  principles of inference. Descartes’s indubitable facts are his own thoughts—using ‘thought’ in the widest possible sense. ‘I think’ is his ultimate premiss. Here the word ‘I’ is really illegitimate; he ought to state his ultimate premiss in the form ‘there are thoughts’. The word ‘I’ is grammatically convenient, but does not describe a datum. When he goes on to say ‘I am a thing which thinks’, he is already using uncritically the apparatus of categories handed down by scholasticism. He nowhere proves that thoughts need a thinker, nor is there reason to believe this except in a grammatical sense.

Bertrand Russell, A History of Western Philosophy

But the decision to regard thoughts, not external object, as prime empirical certainties was very important, and greatly influenced philosophy since then.

How is Descartes’ Philosophy Important?

There are two ways Descartes’ philosophy was important.

It completed the idea of the dualism of mind and matter which started with Plato and was developed, for religious reasons, by Christian philosophy. Barring the strange ideas about the pineal gland and the soul, which were dropped by followers of Descartes, the Cartesian system presents two parallel but independent worlds, that of mind and that of matter, each of which can be studied without reference to the other.

It is not a new idea to say that the mind does not move the body.

There is a considerable discussion in the Meditations as to why the mind feels ‘sorrow’ when the body is thirsty. The correct Cartesian answer was that the body and the mind were like two clocks, and that when one indicated ‘thirst’ the other indicated ‘sorrow’. From the religious point of view, however, there was a grave drawback to this theory; and this brings me to the second characteristic of Cartesianism that I alluded to above.

Bertrand Russell, A History of Western Philosophy

Cartesian was rigidly deterministic as a theory of the material world. If organisms, dead or live, were governed by natural laws, there is no need for a soul to explain the growth of organisms and the movement of animals. Descartes himself allowed an exception; a human soul could choose to alter the direction but the quantity of motion of the vital spirits.  But this is contrary to the spirit of the system and to the laws of mechanics, so it was dropped. Cartesians struggled with free will. And for those who studied Descartes’ science, and not his theory of knowledge, it was reasonable to conclude that animals were automata.

Why not make the leap and say that men are too, and simplify the system? This step was taken in the eighteenth century. In Descartes, there is an unresolved dualism between what he learned from science and what he had learned from theology. This led him into inconsistencies but made him rich in fruitful ideas that completely logical philosophers could not have conceived of.

"Silence is the best expression of scorn" - G.B. Shaw

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