Let us proceed to an immediate consequence of this last observation. If no mechanical definition can be offered for a given term, it is impossible that the things to which this term applies should be governed by mechanical law. We may easily convince ourselves, however, that although not subjected to mechanical law, they are frequently, indeed generally, governed by another kind of law that is of the greatest interest to us. Let me recur to our illustration of the time-piece. There is a trite truth about time-pieces, which we may say holds as a rule, to wit, that cheap time-pieces are poor ones. Yet it would be meaningless to ask for a mechanical explanation of this law, for the mechanical imperfection of the cheap sun dial bears no resemblance whatever to the mechanical imperfection of the cheap watch. The former may be a poor time-keeper because inexpensively (and so grossly) graduated; the latter because the escapement is inexpensively (and so crudely) constructed. So it is in the animal world. Of its members we may lay down the rule, say, that each must eat if it would live, but the physics and chemistry of nutrition in an oak tree are so different from the physics and chemistry of nutrition in a human being, that if anyone were to ask for a mechanical explanation of this rule we could not offer it, or rather we should have to offer a different one for each type of organism we considered. These examples will be sufficient to illustrate the sense of the saying, “Beings whose nature is not capable of mechanical definition cannot be subjected to mechanical law.”