The advance of science is not comparable to the changes of a city, where old edifices are pitilessly torn down to give place to new, but to the continuous evolution of zoologic types which develop ceaselessly and end by becoming unrecognisable to the common sight, but where an expert eye finds always traces of the prior work of the centuries past. One must not think then that the old-fashioned theories have been sterile and vain.

Absolute space, that is to say, the mark to which it would be necessary to refer the earth to know whether it really moves, has no objective existence.... The two propositions: "The earth turns round" and "it is more convenient to suppose the earth turns round" have the same meaning; there is nothing more in the one than in the other.

Mathematicians are born, not made.

One geometry cannot be more true than another; it can only be more convenient.

Later generations will regard Mengenlehre (set theory) as a disease from which one has recovered.

Mathematics is the art of giving the same name to different things.

Sociology is the science with the greatest number of methods and the least results.