Like a _deus ex machina_, or a trick of the trade, it is applied to unloose every knot, and to clear any difficulties that arise. But a principle of this stamp possesses no intimate connexion or organic solidarity with the theory which it helps to prop. It is always at hand as a ready-made schema or heading, and can be attached to the most incongruous orders of fact. Thus in the works of Aristotle, the principle of 'End' or 'Activity' has sometimes seemed to be applied to whatever subject comes forward, and like a hereditary official vestment to suit all its wearers equally well or equally ill. What is true 'on the whole' is not always true 'of each': the _καθόλον_ never quite equals the _καθ' ἔκαστον._ The modern principle of Utility is equally flexible in its application to the problems of moral and social life. It costs no trouble to pronounce the magic word, and even 'such as are of weaker capacity' may make something out of such a formula. But an abstract formula, which is equally applicable to everything, is not particularly applicable to anything. While it seems to save trouble, and is so plain as to be almost tautological (as when the worth of a thing or act is explained to mean its utility), it really suggests fresh questions in every case, and multiplies the difficulty. Having an outward adaptability to every kind of fact, the principle has no true sympathy with any: it becomes a mere form, which we use as we do a measuring-rod, moving it along from one thing to another. We are always reverting to first principles as our last principles also. Even Aristotle, when he remarked that an object had to be criticised from its own principles and not from general formulae, saw through the fallacy of this style of argument. This is like asking for bread and getting a stone. The philosopher, who ought to take us through the shut chambers of the world, merely hands us a key at the gate, telling us that it will unlock every door, and then the insides will speak for themselves. But we would have our philosopher do a little more than this. Not being ourselves omniscient, we should be glad of a guide-book at the least, and perhaps even of the services of an interpreter to explain some peculiarities, some startling phenomena, and sights even more unpleasant than those which appalled the spouse of the notorious Bluebeard. Or, dropping metaphor, we wish the formula to be applied systematically and thoroughly. When that is done the formula loses its abstractness; it gains those necessary amplifications and qualifications, as we call them, without which no theory explains much or gives much information. And thus, instead of fancying that our initial formula contains the truth in a nutshell, we shall find that it is only one step to be taken on the way to truth, and that its narrow statement sinks more and more into insignificance, as its amplified theory gains in significance.