When I consider this carefully, I find not a single property which with certainty separates the waking state from the dream. How can you be certain that your whole life is not a dream?

I am accustomed to sleep and in my dreams to imagine the same things that lunatics imagine when awake.

I think; therefore I am.

Illusory joy is often worth more than genuine sorrow.

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

Common sense is the most fairly distributed thing in the world, for each one thinks he is so well-endowed with it that even those who are hardest to satisfy in all other matters are not in the habit of desiring more of it than they already have.