I accept no principles of physics which are not also accepted in mathematics.

The reading of all good books is like a conversation with the finest minds of past centuries.

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

For how do we know that the thoughts which occur in dreaming are false rather than those others which we experience when awake, since the former are often not less vivid and distinct than the latter?

On the one hand I have a clear and distinct idea of myself, in so far as I am a thinking, non-extended thing; and on the other hand I have a distinct idea of body, in so far a this is simply an extended, non-thinking thing. And, accordingly, it is certain that I am really distinct from my body, and exist without it.

If I simply refrain from making a judgment in cases where I do not perceive the truth with sufficient clarity and distinctness, then it is clear that I am behaving correctly and avoiding error.

Few look for truth; many prowl about for a reputation of profundity by arrogantly challenging whichever arguments are the best.