You will understand this better, perhaps, if I give you some familiar example.  You have all heard it repeated, I dare say, that men of science work by means of induction and deduction, and that by the help of these operations, they, in a sort of sense, wring from Nature certain other things, which are called natural laws, and causes, and that out of these, by some cunning skill of their own, they build up hypotheses and theories.  And it is imagined by many, that the operations of the common mind can be by no means compared with these processes, and that they have to be acquired by a sort of special apprenticeship to the craft.  To hear all these large words, you would think that the mind of a man of science must be constituted differently from that of his fellow men; but if you will not be frightened by terms, you will discover that you are quite wrong, and that all these terrible apparatus [87] are being used by yourselves every day and every hour of your lives.

There is a well-known incident in one of Moliere’s plays,[88] where the author makes the hero express unbounded delight on being told that he had been talking prose during the whole of his life.  In the same way, I trust, that you will take comfort, and be delighted with yourselves, on the discovery that you have been acting on the principles of inductive and deductive philosophy during the same period.  Probably there is not one here who has not in the course of the day had occasion to set in motion a complex train of reasoning, of the very same kind, though differing of course in degree, as that which a scientific man goes through in tracing the causes of natural phenomena.

A very trivial circumstance will serve to exemplify this.  Suppose you go into a fruiterer’s shop, wanting an apple,—­you take up one, and, on biting it, you find it is sour; you look at it, and see that it is hard and green.  You take up another one, and that too is hard, green, and sour.  The shopman offers you a third; but, before biting it, you examine it, and find that it is hard and green, and you immediately say that you will not have it, as it must be sour, like those that you have already tried.

Nothing can be more simple than that, you think; but if you will take the trouble to analyse and trace out into its logical elements what has been done by the mind, you will be greatly surprised.  In the first place you have performed the operation of induction.  You found that, in two experiences, hardness and greenness in apples went together with sourness.  It was so in the first case, and it was confirmed by the second.  True, it is a very small basis, but still it is enough to make an induction from; you generalise the facts, and you expect to find sourness in apples where you get hardness and greenness.  You found upon that a general law that all hard and green apples are sour; and that, so far as it goes, is a perfect induction.  Well, having got your natural law in this way, when you are offered another apple which