The philosophy of Rene Descartes

DOUBT, not scepticism, was Descartes's philosophic starting point. Warned by the fate of Galileo, he withheld from publication during his lifetime his treatise on The World which he had finished in 1633. His search after philosophical certainty is explained in the Discourse on Method published in 1637. In 1641 he published Meditationes de Prima Philosophia, and he dealt with morals in Principia Philosophiae, and Traite des Passions de L'Ame. Descartes stands at the head of the school of mathematicians which linked up the mathematics of the Renaissance with modern mathematical writings. The invention of analytical geometry dates from the publication of his Geometry. His Discourse on Method is a landmark in the modern history of philosophic thought.


GOOD sense or reason must be better distributed than anything else in the world, for no man desires more of it than he already has. This shows that reason is by nature equal in all men. If there is diversity of opinion, this arises from the fact that we conduct our thought by different ways and consider not the same things. It does not suffice that the understanding be good--it must be well applied.

My mind is no better than another's, but I have been lucky enough to chance on certain ways, which have led me to a certain method by means of which it seems to me that I may by degrees augment my knowledge to the modest measure of my intellect and my length of days. I shall be very glad to make plain in this Discourse the paths I have followed, and to picture my life so that all may judge of it, and by the setting forth of their opinions may furnish me with yet other means of improvement.

It is my design not to teach the method which each man ought to follow for the right guidance of his reason, but only to show in what manner I have tried to conduct my own.

I had been nourished on letters from my infancy, but as soon as I had finished the customary course of study, I found myself hampered by so many doubts and errors that I seemed to have reaped no benefits, except that I had observed more and more of my ignorance. Yet I was at one of the most celebrated schools in Europe, and I was not held inferior to my fellow-students, some of whom were destined to take the place of our masters; nor did our age seem less fruitful of good wits than any which had gone before.

Though I did not cease to esteem the studies of the schools, I began to think that I had given enough time to languages, enough also to ancient books, their stories and their fables; for when a man spends too much time in travelling abroad he becomes a stranger in his own country; and so, when he is too curious concerning what went on in past ages, he is apt to remain ignorant of what is taking place in his own day. I set a high price on eloquence, and I was in love with poetry; I rejoiced in mathematics, but knew nothing of its true use.

I revered our theology, but, since the way to heaven lies open to the ignorant no less than to the learned, and the revealed truths which lead thither are beyond our intelligence, I did not dare to submit them to my feeble reasonings.

In philosophy there is no truth which is not disputed and which, consequently, is not doubtful; the other sciences all borrow their principles from philosophy.

Therefore, I entirely gave up the study of letters and employed the rest of my youth in travelling, being resolved to seek no other science than that which I might find within myself, or in the great Book of the World.

Here the best lesson that I learnt was not to believe too firmly anything of which I had learnt merely by example and custom; and thus little by little was delivered from many errors which are liable to obscure the light of nature and to diminish our capacity of hearing reason. Finally, I resolved one day to study myself in the same way, and in this it seems to me I succeeded much better than if I had never departed from either my country or my books.


BEING in Germany, on my way to rejoin the army after the coronation of the Emperor [Ferdinand II], I was lying at an inn where, in default of other conversation, I was at liberty to entertain my own thoughts. Of these, one of the first was that often there is less perfection in works which are composite than in those which issue from a single hand. Such was the case with buildings, cities, states; for a people which has made its laws from time to time to meet particular occasions will enjoy a less perfect polity than a people which from the beginning has observed the constitution of a far-sighted legislator. This is very certain, that the estate of true religion, which God alone has ordained, must be incomparably better guided than any other.

And again, I considered that as, during our childhood, we had been governed by our appetites and our tutors, which are often at variance, which neither of them perhaps always gave us the best counsel, it is almost impossible that our judgments should be so pure and so solid as they would have been if we had had the perfect use of our reason from the time of our birth and had never been guided by anything else.

Hence, as regarded the opinions that I had received into my belief, I thought that, as a private person may pull down his own house to build a finer, so I could not do better than remove them therefrom in order to replace them by sounder, or, after I should have adjusted them to the level of reason, to establish the same once more.

When I was younger I had studied logic, analytical geometry and algebra. Of these, I found that logic served rather for explaining things we already know; while of geometry and algebra, the former is so tied to the consideration of figures that it cannot exercise the understanding without wearying the imagination, and the latter is so bound down to certain rules and ciphers that it has been made a confused and obscure art which hampers the mind instead of a science which cultivates it. And as a state is better governed which has but few laws, and those strictly observed, I believed that I should find sufficient these four precepts:

THE first was never to accept anything as true when I did not recognize it clearly to be so--that is to say, carefully to avoid precipitation and prejudice, but to include in my opinions nothing beyond that which should present itself so clearly and distinctly to my mind that I might have no occasion to doubt it.

The second was to divide up the difficulties which I should examine into as many parts as possible, and as should be required for their better solution.

The third was to conduct my thoughts in order, by beginning with the simplest objects, so as to mount little by little, by stages, to the most complex knowledge, even supposing an order among things which did not naturally stand in an order of antecedent and consequent.

And the last was to make every where enumerations so complete, and surveys so wide, that I should be sure of omitting nothing.

Exact observation of these precepts gave me such facility in unravelling the questions comprehended in geometrical analysis and in algebra, that in two or three months not only did I find my way through many which I had formerly accounted too hard for me, but, towards the end, I seemed to be able to determine, in those which were new to me, by what means and to what extent it was possible to resolve them.

And so I promised myself that I would apply my system with equal success to the difficulties of other sciences; but since their principles must all be borrowed from philosophy, in which I found no certain principles of its own, I thought that before all else I must try to establish some therein. By way of preparation (for I was then but twenty-three years old) I must root up from my mind my previous bad opinion of it, and must practise my method in order that I might be confirmed in it.

Return to Outline of Great Books Volume I