This truth can be yet further elucidated by means of Mill’s two other illustrations. If the two blades of a pair of scissors were made of two different materials, and the one blade were of such a nature that it was always of the same quality, and human ingenuity was not capable of improving it, whilst the qualities of the other blade varied with the skill devoted to its manufacture, and if one pair of scissors should cut twenty yards of cloth in a minute, whilst another cut only ten, the additional {200} efficiency of the more efficient pair would, it is perfectly obvious, be due to that blade in respect of which this pair differed from the pair which was less efficient, not to the blade in respect of which both pairs were similar. Again, let us take Mill’s case of the two numerals five and six. If five is always to be the number multiplied, and six is always to be the multiplier, it is true we cannot say which does most in producing the result—thirty. But if the number to be multiplied remains always five, whilst the multiplying number varies—if it is in one case six and in another case ten,—and if the result of the multiplication in the second case is not thirty but fifty, it is obvious that the additional twenty which results from our multiplying by ten is due not to any change in the number multiplied, but to the additional four introduced into the number multiplying. To these illustrations we may add two others—the movement of a modern bicycle and the movement of a man running. A modern bicycle cannot be propelled without a chain; and if there were only one kind of bicycle in the world, Mill might fairly have said that it was meaningless and useless to ask whether the wheels or the chain contributed most to its velocity. But if there are two bicycles, with precisely similar wheels, but with dissimilar chains, and if the same man riding on one can accomplish ten miles an hour only, but on the other fifteen, the common sense of every bicycle rider in the world will tell him that the additional five miles are contributed entirely by the chain, and {201} the patentees of the chain, we may be certain, will add their valuable testimony to the fact. So with regard to running, Mill might fairly have said that if we consider it in an abstract and general sense, it is absurd to ask which contributes most to “_the effect_”—the ground or the man that runs on it, because the first is as indispensable to the man’s movement as is the second. But if two men are racing each other over the same course, and one runs a mile whilst the other runs only half, it is perfectly obvious that the extra speed of the winner is contributed not by the ground, which for both men is just the same, but by certain qualities in the winner which the loser does not possess, or which the winner possesses in larger measure than he.