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.

I concluded that I might take as a general rule the principle that all things which we very clearly and obviously conceive are true: only observing, however, that there is some difficulty in rightly determining the objects which we distinctly conceive.

If I go for the alternative which is false, then obviously I shall be in error; if I take the other side, then it is by... chance that I arrive at the truth, and I shall still be at fault.... In this incorrect use of free will may be found the privation which constitutes the essence of error.

Wonder is the first of all the passions.

So far, I have been a spectator in this theater which is the world, but I am now about to mount the stage, and I come forward masked.

It is possible that I am dreaming right now and that all of my perceptions are false.

Instead I ought to be grateful to Him who never owed me anything for having been so generous to me, rather than think that He deprived me of those things or has taken away from me whatever He did not give me.