A first fact should surprise us, or rather would surprise us if we were not used to it. How does it happen there are people who do not understand mathematics? If mathematics invokes only the rules of logic, such as are accepted by all normal minds...how does it come about that so many persons are here refractory?

Doubting everything and believing everything are two equally convenient solutions that guard us from having to think

Ideas rose in clouds; I felt them collide until pairs interlocked, so to speak, making a stable combination.

It is far better to foresee even without certainty than not to foresee at all.

Mathematical discoveries, small or great are never born of spontaneous generation.

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.

A cat is witty, he has nerve, he knows how to do precisely the right thing at the right moment.