Nature has neither core nor skin: she’s both at once outside and in.

A flippant, frivolous man may ridicule others, may controvert them, scorn them; but he who has any respect for himself seems to have renounced the right of thinking meanly of others.

The use of a thing is only a part of its significance. To know anything thoroughly, to have the full command of it in all its appliances, we must study it on its own account, independently of any special application.

As for what I have done as a poet, I take no pride in whatever. Excellent poets have lived at the same time with me, poets more excellent lived before me, and others will come after me. But that in my country I am the only person who knows the truth in the difficult science of colors-of that, I say, I am not a little proud, and here have a consciousness of superiority to many.

In comradeship is danger countered best.

Deny yourself! You must deny yourself! That is the song that never ends.

Mathematics has the completely false reputation of yielding infallible conclusions. Its infallibility is nothing but identity. Two times two is not four, but it is just two times two, and that is what we call four for short. But four is nothing new at all. And thus it goes on and on in its conclusions, except that in the higher formulas the identity fades out of sight.