The true definition of madness is repeating the same action, over and over, hoping for a different result.

We come now to the question: what is a priori certain or necessary, respectively in geometry (doctrine of space) or its foundations? Formerly we thought everything; nowadays we think nothing. Already the distance-concept is logically arbitrary; there need be no things that correspond to it, even approximately.

I am not a Jew in the sense that I would demand the preservation of the Jewish or any other nationality as an end in itself. Rather, I see Jewish nationality as a fact and I believe that every Jew must draw the consequences from this fact.

The greatest activity of which man is capable: Opening up yet another fragment of the frontier of beauty.

Human knowledge and skills alone cannot lead humanity to a happy and dignified life. Humanity has every reason to place the proclaimers of high moral standards and values above the discoverers of objective truth.

In their struggle for the ethical good, teachers of religion must have the stature to give up the doctrine of a personal god, that is, give up that source of fear and hope which in the past placed such vast power in the hands of priests. In their labors they will have to avail themselves of those forces which are capable of cultivating the Good, the True, and the Beautiful in humanity itself. This is, to be sure, a more difficult but an incomparably more worthy task.

There is separation of colored people from white people in the United States. That separation is not a disease of colored people. It is a disease of white people. I do not intend to be quiet about it.