Nothing comes out of nothing.

If I found any new truths in the sciences, I can say that they follow from, or depend on, five or six principal problems which I succeeded in solving and which I regard as so many battles where the fortunes of war were on my side.

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

Everything is self-evident.

We do not describe the world we see, we see the world we can describe.

God alone is the author of all the motions in the world.