Nature will not forgive those who fail to fulfill the law of their being. The law of human beings is wisdom and goodness, not unlimited acquisition.

A civilization in which there is not a continuous controversy about important issues is on the way to totalitarianism and death

It is not so important to be serious as it is to be serious about the important things.

To solve a problem it is necessary to think. It is necessary to think even to decide what facts to collect.

Every act of every man is a moral act, to be tested by moral, and not by economic criteria.

Education is a kind of continuing dialogue, and a dialogue assumes different points of view.

Mathematics ... is indispensable as an intellectual technique. In many subjects, to think at all is to think like a mathematician.