René Descartes

I have no doubt that I am something.

I found myself constrained to confess that there is a God, and that He is a perfect being.

The long chains of simple and easy reasonings by means of which geometers are accustomed to reach the conclusions of their most difficult demonstrations, had led me to imagine that all things, the knowledge of which is within the reach of man, are mutually connected in the same way.

I resolved to seek no other knowledge than that which could be found in myself, or at least in the great book of the world.

I concluded that I was a substance whose whole essence or nature consists only in thinking, and which, in order to exist, has no need of any place nor depends on any material thing.

I have never made any discoveries that were not the result of my own thoughts.

The will is by its nature so free that it can never be constrained.

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

I consider that I have no senses, that body, figure, extension, motion, and place are nothing but fictions of my mind.

It is true that I have a body, but it is not true that I am my body.

I have always held that the existence of God and of the human soul are the principal matters of philosophy.

I have learned to distrust my senses.

I am certain that I am a thinking thing, and that I exist.

The mind is more easily known than the body.

Except for our own thoughts, there is nothing absolutely in our power.

I have been nourished by the study of letters since my childhood, and since I was assured that by their means one could acquire a clear and certain knowledge of all that is useful for life, I had an extreme desire to learn them.

Doubt is the origin of wisdom.

I desire to live in peace and to be useful to the world.

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

The greatest good is to live without fear, and to be free from the passions.