Science is organized common sense where many a beautiful theory was killed by an ugly fact.

Common sense is science exactly in so far as it fulfills the ideal of common sense; that is, sees facts as they are, or at any rate, without the distortion of prejudice, and reasons from them in accordance with the dictates of sound judgment. And science is simply common sense at its best, that is, rigidly accurate in observation, and merciless to fallacy in logic.

The chess-board is the world, the pieces are the phenomena of the universe, the rules of the game are what we call the laws of Nature. The player on the other side is hidden from us.

I hated tobacco. I could have almost lent my support to any institution that had for its object the putting of tobacco smokers to death...I now feel that smoking in moderation is a comfortable and laudable practice, and is productive of good. There is no more harm in a pipe than in a cup of tea. You may poison yourself by drinking too much green tea, and kill yourself by eating too many beefsteaks. For my part, I consider that tobacco, in moderation, is a sweetener and equalizer of the temper.

My business is to teach my aspirations to confirm themselves to fact, not to try and make facts harmonize with my aspirations.

Though under-instruction is a bad thing, it is not impossible that over-instruction may be worse.

History warns us that it is the customary fate of new truths to begin as heresies and to end as superstitions.