Science is practical philosophy.

To live without philosophizing is in truth the same as keeping the eyes closed without attempting to open them.

Intuition is the undoubting conception of a pure and attentive mind, which arises from the light of reason alone, and is more certain than deduction.

My third maxim was to try always to conquer myself rather than fortune, and to change my desires rather than the order of the world, and generally to accustom myself to believing that there is nothing entirely in our power except our thoughts, so that after we have done our best regarding things external to us, everything in which we do not succeed is for us absolutely impossible.

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.

It must not be thought that it is ever possible to reach the interior earth by any perseverance in mining: both because the exterior earth is too thick, in comparison with human strength; and especially because of the intermediate waters, which would gush forth with greater impetus, the deeper the place in which their veins were first opened; and which would drown all miners.

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