Rene Descartes

I have always taken the greatest pleasure in mathematics.

The senses alone are not sufficient to give us a clear and distinct knowledge of things.

I am a thing that thinks, that doubts, that affirms, that denies, that wills, that refuses, that imagines also, and that perceives.

I consider that I possess no senses; I imagine that body, figure, extension, motion and place are but fictions of my mind.

The existence of God is demonstrated by the fact that I have an idea of a perfect being.

I believe that all my dreams are illusions.

The existence of God is as evident as that of a triangle.

Perfect numbers like perfect men are very rare.

The first precept was never to accept a thing as true until I knew it as such without a single doubt.

The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once.

The preservation of health has always been the principal end of my studies.

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

The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge.

Travelling is almost like talking with those of other centuries.

I entirely abandoned the study of letters, resolving to seek no other science than that which could be found in myself, or at least in the great book of the world.

I think, therefore I am — this is the first and most certain conclusion that anyone who philosophizes in order should arrive at.

I suppose therefore that all I see is false. I believe that none of what my deceptive memory represents to me ever existed.

I desire to live in peace and to be useful to all men.

It is precisely because I am in the habit of using my senses to think of things that I find it difficult to think of anything else.

I confess that I have never been able to find out what is the 'substantial form' of a human body, or how it differs from the form of a statue.