René Descartes

The human mind is capable of knowing all things, if it only applies itself to them.

The purpose of philosophy is to find the truth.

The soul is united to all the parts of the body, but it exercises its functions more particularly in the brain.

I am not a body, but a thinking thing.

The existence of God is as certain as any geometrical demonstration.

The world is full of wonders, but they are not always visible to the naked eye.

The true beauty of things lies in their order and arrangement.

But what then am I? A thinking thing. What is a thinking thing? It is a thing that doubts, understands, affirms, denies, wills, refuses, imagines also, and perceives.

I saw that from the very fact that I thought of doubting the truth of other things, it followed very certainly and obviously that I existed.

I am a substance whose whole essence or nature is to think, and whose being does not depend on any material thing.

I have always been of the opinion that the two questions, God and the Soul, were the most important of those that ought to be demonstrated by means of philosophy rather than theology.

I suppose therefore that all the things I see are false; I believe that none of those things ever existed that my deceptive memory represents to me; I believe that I have no senses; I believe that body, figure, extension, movement and place are nothing but fictions of my mind.

I entirely reject and despise all the reasonings of the Skeptics, who doubt of everything, even of the first principles of knowledge.

It is possible that I am dreaming, and that all my perceptions are false.

The existence of God is demonstrated by the very idea of God as a perfect being.

I observed that, while I thus wished to think that everything was false, it was necessary that I, who thought thus, should be something.

I concluded that I was a substance whose whole essence or nature consists only in thinking, and that, in order to be, it needs no place and depends on no material thing.

I resolved to seek no other knowledge than that which I might find within myself, or perhaps in the great book of the world.

I have no doubt that I am a thinking substance, and that I have a clear and distinct idea of myself as a thinking substance.

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