How do we know that anything really exists, that anything is really the way it seems ot us through our senses?

Illusory joy is often worth more than genuine sorrow.

But in my opinion, all things in nature occur mathematically.

Divide each difficulty at hand into as many pieces as possible and as could be required to better solve them.

Common sense is the most widely shared commodity in the world, for every man is convinced that he is well supplied with it.

When writing about transcendental issues, be transcendentally clear.

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.