He who hid well, lived well.

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

Variant: When it is not in our power to follow what is true, we ought to follow what is most probable.

Hence reason also demands that, since our thoughts cannot all be true because we are not wholly perfect, what truth they do possess must inevitably be found in the thoughts we have when awake, rather than in our dreams.

This result could have been achieved either by his [God] endowing my intellect with a clear and distinct perception of everything about which I would ever deliberate, or simply by impressing the following rule so firmly upon my memory that I could never forget it: I should never judge anything that I do not clearly and distinctly understand.

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

I can doubt everything, except one thing, and that is the very fact that I doubt. Simply put - I think, therefore I am