Although my knowledge grows more and more, nevertheless I do not for that reason believe that it can ever be actually infinite, since it can never reach a point so high that it will be unable to attain any greater increase.

All is to be doubted.

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.

The only thing that I know, is that I know nothing

The principal effect of the passions is that they incite and persuade the mind to will the events for which they prepared the body.

I know that I exist; the question is, What is this 'I' that 'I' know.

If ... it is not in my power to arrive at the knowledge of any truth, I may at least do what is in my power, namely, suspend judgement.