The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful. If … - Henri Poincaré

Je ne sais si je n’ai déjà dit quelque part que la Mathématique est l’art de donner le même nom à des choses différentes.

In general, the totality A will have nothing in common with the totality A´, nor the totality B with the totality B´. The transition from the totality A to the totality B and that from the totality A´ to the totality B´ are therefore two changes which in themselves have in general nothing in common. And yet we regard these two changes both as displacements and, furthermore, we consider them as the same displacement. How can that be? It is simply because they can both be corrected by the same correlative movement of our body.

Thought is only a flash between two long nights, but this flash is everything.