A thing is not proved just because no one has ever questioned it. What has never been gone into impartially has never been properly gone into. Hence scepticism is the first step toward truth. It must be applied generally, because it is the touchstone.

The most dangerous madmen are those created by religion, and people whose aim is to disrupt society always know how to make good use of them on occasion.

I picture the vast realm of the sciences as an immense landscape scattered with patches of dark and light. The goal towards which we must work is either to extend the boundaries of the patches of light, or to increase their number. One of these tasks falls to the creative genius; the other requires a sort of sagacity combined with perfectionism.

If you disturb the colors of the rainbow, the rainbow is no longer beautiful.

One may demand of me that I should seek truth, but not that I should find it

How old the world is! I walk between two eternities.... What is my fleeting existence in comparison with that decaying rock, that valley digging its channel ever deeper, that forest that is tottering and those great masses above my head about to fall? I see the marble of tombs crumbling into dust; and yet I don't want to die!

I discuss with myself questions of politics, love, taste, or philosophy. I let my mind rove wantonly, give it free rein to followany idea, wise or mad that may present itself. My ideas are my harlots.