The range of human knowledge today is so great that we're all specialists and the distance between specializations has become so great that anyone who seeks to wander freely between them almost has to forego closeness with the people around him.

One geometry cannot be more true than another; it can only be more convenient. Geometry is not true, it is advantageous.

When you've got a Chautauqua in your head, it's extremely hard not to inflict it on innocent people.

Laws of nature are human inventions, like ghosts. Laws of logic, or mathematics are also human inventions, like ghosts. The whole blessed thing is a human invention, including the idea that it isn't a human invention.

In the high country of the mind one has to become adjusted to the thinner air of uncertainty.

Quality... you know what it is, yet you don't know what it is.

The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed.