Rene Descartes

We never understand a thing so well, and make it our own, as when we have discovered it for ourselves.  - Rene Descartes

I think therefore I am. (Cogito ergo sum) - Rene Descartes

Each problem that I solved became a rule which served afterwards to solve other problems.  - Rene Descartes, "Discours de la Methode"