Sensations are nothing but confused modes of thinking.

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

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

Science is practical philosophy.

Mathematics is a more powerful instrument of knowledge than any other that has been bequeathed to us by human agency.

I did not imitate the skeptics who doubt only for doubting's sake, and pretend to be always undecided; on the contrary, my whole intention was to arrive at a certainty, and to dig away the drift and the sand until I reached the rock or the clay beneath.

... regard this body as a machine which, having been made by the hand of God, is incomparably better ordered than any machine that can be devised by man, and contains in itself movements more wonderful than those in any machine. ... it is for all practical purposes impossible for a machine to have enough organs to make it act in all the contingencies of life in the way in which our reason makes us act.