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

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 think; therefore I am.

I experienced in myself a certain capacity for judging which I have doubtless received from God, like all the other things that I possess; and as He could not desire to deceive me, it is clear that He has not given me a faculty that will lead me to err if I use it aright.

There is nothing so strange and so unbelievable that it has not been said by one philosopher or another.

But in my opinion, all things in nature occur mathematically.

The mind effortlessly and automatically takes in new ideas, which remain in limbo until verified or rejected by conscious, rational analysis.