Desire awakens only to things that are thought possible.

I did not imitate the skeptics who doubt only for doubting's sake, and pretend to be always undecided; on the contrary, my whole intention was to arrive at a certainty, and to dig away the drift and the sand until I reached the rock or the clay beneath.

... moral certainty is certainty which is sufficient to regulate our behaviour, or which measures up to the certainty we have on matters relating to the conduct of life which we never normally doubt, though we know that it is possible, absolutely speaking, that they may be false.

Even if I were to suppose that I was dreaming and whatever I saw or imagined was false, yet I could not deny that ideas were truly in my mind.

If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.

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

To live without philosophizing is in truth the same as keeping the eyes closed without attempting to open them.