I suppose therefore that all things I see are illusions; I believe that nothing has ever existed of everything my lying memory tells me. I think I have no senses. I believe that body, shape, extension, motion, location are functions. What is there then that can be taken as true? Perhaps only this one thing, that nothing at all is certain.

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.

In the matter of a difficult question it is more likely that the truth should have been discovered by the few than by the many.

It is to the body alone that we should attribute everything that can be observed in us to oppose our reason.

Let whoever can do so deceive me, he will never bring it about that I am nothing, so long as I continue to think I am something.

The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once.

Even those who have the weakest souls could acquire absolute mastery over all their passions if we employed sufficient ingenuity in training and guiding them.