Doubt is the beginning, not the end, of wisdom.

They will listen with both ears to what is said by the men just a step or two ahead of them, who stand nearest to them, and within arm's reach. A guide ceases to be of any use when he strides so far ahead as to be hidden by the curvature of the earth.

We despair of changing the habits of men, still we would alter institutions, the habits of millions of men.

Some young folks have wind-fall minds, prematurely detached from the tree of knowledge for a life-long sourness and pettiness.

To render aid to the worthless is sheer waste. Rain does not freshen the Dead Sea, but only enables it to dissolve more salt.

Boundaries which mark off one field of science from another are purely artificial, are set up only for temporary convenience. Let chemists and physicists dig deep enough, and they reach common ground.

When we try to imagine a chaos we fail. ... In its very fiber the mind is an order and refuses to build a chaos.