Fertility of imagination and abundance of guesses at truth are among the first requisites of discovery; but the erroneous guesses must almost of necessity be many times as numerous as those which prove well founded.

The whole value of science consists in the power which it confers upon us of applying to one object the knowledge acquired from like objects; and it is only so far, therefore, as we can discover and register resemblances that we can turn our observations to account.

It is clear that economics, if it is to be a science at all, must be a mathematical science.

The child which overbalances itself in learning to walk is experimenting on the law of gravity.

Charles Babbage proposed to make an automaton chess-player which should register mechanically the number of games lost and gained in consequence of every sort of move. Thus, the longer the automaton went on playing game, the more experienced it would become by the accumulation of experimental results. Such a machine precisely represents the acquirement of experience by our nervous organization.

When quite young I can remember I had no thought or wish of surpassing others. I was rather taken with a liking of little arts and bits of learning. My mother carefully fostered a liking for botany, giving me a small microscope and many books, which I yet have. Strange as it may seem, I now believe that botany and the natural system, by exercising discrimination of kinds, is the best of logical exercises. What I may do in logic is perhaps derived from that early attention to botany.

Value is the most invincible and impalpable of ghosts, and comes and goes unthought of, while the visible and dense matter remains as it was.