There is a great difference between mind and body insomuch as body is by nature always divisible, and the mind is entirely indivisible.

Whatever I have up till now accepted as most true and assured I have gotten either from the senses or through the senses. But from time to time I have found that the senses deceive, and it is prudent never to trust completely those who have deceived us even once.

How can you be certain that your whole life is not a dream?

The greatest minds are capable of the greatest vices as well as of the greatest virtues.

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

What then is the source of my errors? They are owing simply to the fact that, since the will extends further than the intellect, I do not contain the will within the same boundaries; rather, I also extend it to things I do not understand. Because the will is indifferent in regard to such matters, it easily turns away from the true and the good; and in this way I am deceived and I sin.

Mathematics is a more powerful instrument of knowledge than any other that has been bequeathed to us by human agency.