The guiding motto in the life of every natural philosopher should be, seek simplicity and distrust it.

You think the world is what it looks like in fine weather at noon day; I think it is what it seems like in the early morning when one first wakes from deep sleep.

There is a technique, a knack, for thinking, just as there is for doing other things. You are not wholly at the mercy of your thoughts, any more than they are you. They are a machine you can learn to operate.

An open mind is all very well in its way, but it ought not to be so open that there is no keeping anything in or out of it.

In every age of well-marked transition, there is the pattern of habitual dumb practice and emotion which is passing and there is oncoming a new complex of habit.

It is natural to think that an abstract science cannot be of much importance in affairs of human life, because it has omitted from its consideration everything of real interest.

The tragedy of the world is that those who are imaginative have but slight experience, and those who are experienced have feeble imaginations.