Science, by itself, cannot supply us with an ethic. It can show us how to achieve a given end, and it may show us that some ends cannot be achieved.

The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts.

Boys and young men acquire readily the moral sentiments of their social milieu, whatever these sentiments may be.

In emancipation from the fears that beset the slave of circumstance he will experience a profound joy, and through all the vicissitudes of his outward life he will remain in the depths of his being a happy man.

When one admits that nothing is certain one must, I think, also admit that some things are much more nearly certain than others.

The rules of logic are to mathematics what those of structure are to architecture.

The fact that an opinion has been widely held is no evidence whatever that it is not utterly absurd.