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.

The first precept was never to accept a thing as true until I knew it as such without a single doubt.

I am indeed amazed when I consider how weak my mind is and how prone to error.

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.

There is nothing so strange and so unbelievable that it has not been said by one philosopher or another.

An optimist may see a light where there is none, but why must the pessimist always run to blow it out?

... regard this body as a machine which, having been made by the hand of God, is incomparably better ordered than any machine that can be devised by man, and contains in itself movements more wonderful than those in any machine. ... it is for all practical purposes impossible for a machine to have enough organs to make it act in all the contingencies of life in the way in which our reason makes us act.