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.

Each problem that I solved became a rule, which served afterwards to solve other problems.

Except our own thoughts, there is nothing absolutely in our power.

Desire awakens only to things that are thought possible.

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

Truths are more likely to be discovered by one man than by a nation

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