The mind effortlessly and automatically takes in new ideas, which remain in limbo until verified or rejected by conscious, rational analysis.

Neither the true nor the false roots are always real; sometimes they are imaginary; that is, while we can always imagine as many roots for each equation as I have assigned, yet there is not always a definite quantity corresponding to each root we have imagined.

And as it is the most generous souls who have most gratitude, it is those who have most pride, and who are most base and infirm, who most allow themselves to be carried away by anger and hatred.

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?

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.

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

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.