The penalty of death is the only one that makes an injustice absolutely irreparable; from which it follows that the existence of the death penalty implies that one is exposed to committing an irreparable injustice; from which it follows that it is unjust to establish it. This reasoning appears to us to have the force of a demonstration.

I hope to see the bringing together of all the best educated people of the earth into a worldwide Congress of Scientists.

The truth belongs to those who seek it, not to those who claim to own it.

Men do not often dare to avow, even to themselves, the slow progress reason has made in their minds; but they are ready to follow it if it is presented to them in a lively and striking manner, and forces them to recognize it.

[All phenomena] are equally susceptible of being calculated, and all that is necessary, to reduce the whole of nature to laws similar to those which Newton discovered with the aid of the calculus, is to have a sufficient number of observations and a mathematics that is complex enough.

People still retain the errors of their childhood, their nation, and their age, long after they have accepted the truths needed to refute them.

If it is possible to have a linear unit that depends on no other quantity, it would seem natural to prefer it. Moreover, a mensural unit taken from the earth itself offers another advantage, that of being perfectly analogous to all the real measurements that in ordinary usage are also made upon the earth, such as the distance between two places or the area of some tract, for example. It is far more natural in practice to refer geographical distances to a quadrant of a great circle than to the length of a pendulum.