René Descartes

I shall never be a philosopher if I have a good memory.

The whole of philosophy is like a tree: the roots are metaphysics, the trunk is physics, and the branches that issue from the trunk are all the other sciences.

There is nothing so far removed from us to be beyond our reach, or so hidden that we cannot discover it.

To know what people really think, pay regard to what they do, rather than what they say.

It is a mark of prudence never to place our complete trust in those who have deceived us even once.

The preservation of health should be the primary study.

I am indeed amazed when I consider how weak my mind is and how prone to error.

Whenever anyone has offended me, I try to raise my soul so high that the offense cannot reach it.

The chief cause of human errors is to be found in the prejudices picked up in childhood.

I resolved to pretend that all the things that had ever entered my mind were no more true than the illusions of my dreams.

It is not possible that a deceiver who is supremely powerful and cunning should employ his whole energies in deceiving me; for then I should undoubtedly exist.

The greatest pleasure I know is to do a good action by stealth, and to have it found out by accident.

In order to improve the mind, we ought less to learn, than to contemplate.

The first was never to accept anything for true which I did not clearly know to be such; that is to say, carefully to avoid precipitancy and prejudice, and to comprise nothing more in my judgment than what was presented to my mind so clearly and distinctly as to exclude all ground of doubt.

I can doubt everything, except one thing, and that is the very fact that I doubt.

The nature of matter, or body considered in general, consists not in its being something which is hard or heavy or coloured, or which affects the senses in any way, but simply in its being something which is extended in length, breadth and depth.

I desire to live in peace and to continue the life I have begun under the motto 'to live well you must live unseen'.

It is only the great souls who are capable of great vices as well as great virtues.

The mind depends so much on the temperament and disposition of the bodily organs that, if it is possible to find a means of rendering men wiser and cleverer than they have hitherto been, I believe that it is in medicine that it must be sought.

I am not one of those who believe that the soul is immortal by nature; I see no necessity for that.