Bad books engender bad habits, but bad habits engender good books.

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.

Divide each difficulty into as many parts as is feasible and necessary to resolve it.

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

De omnibus dubitandum

The greatest minds are capable of the greatest vices as well as of the greatest virtues.

I am thinking, therefore I exist. (...) I was a substance whose whole essence or nature is solely to think, and which does not require any place, or depend on any material thing, in order to exist. Accordingly this 'I' - that is, the soul by which I am what I am - is entirely distinct from the body, and indeed is easier to know than the body, and would not fail to be whatever it is, even if the body did not exist.