Those theories of Ethics, then, are naturalistic which declare the sole good to consist in some one property of things, which exists in time; and which do so because they suppose that good itself can be defined by reference to such a property. And we may now proceed to consider such theories. (§ 27 ¶ 1)

And, first of all, one of the most famous of ethical maxims is that which recommends a life according to nature. That was the principle of the Stoic Ethics; but, since their Ethics has some claim to be called metaphysical, I shall not attempt to deal with it here. But the same phrase reappears in Rousseau; and it is not unfrequently maintained even now that what we ought to do is live naturally. Now let us examine this contention in its general form. It is obvious, in the first place, that we cannot say that everything natural is good, except perhaps in virtue of some metaphysical theory, such as I shall deal with later. If everything natural is equally good, then certainly Ethics, as it is ordinarily understood, disappears; for nothing is more certain, from an ethical point of view, than that some things are bad and others good; the object of Ethics is, indeed, in chief part, to give you general rules whereby you may avoid the one and secure the other. What, then, does natural mean, in this advice to live naturally, since it obviously cannot apply to everything that is natural? (§ 27 ¶ 2)

The phrase seems to point to a vague notion that there is some such thing as natural good; to a belief that Nature may be said to fix and decide what shall be good, just as she fixes and decides what shall exist. For instance, it may be supposed that health is susceptible of a natural definition, that Nature has fixed what health shall be: and health, it may be said, is obviously good; hence in this case Nature has decided the matter; we have only to go to her and ask her what health is, and we shall know what is good: we shall have based an ethics upon science. But what is this natural definition of health? I can only conceive that health should be defined in natural terms as the normal state of an organism; for undoubtedly disease is also a natural product. To say that health is what is preserved by evolution, and what itself tends to preserve, in the struggle for existence, the organism which possesses it, comes to the same thing: for the point of evolution is that it pretends to give a causal explanation of why some forms of life are normal and others are abnormal; it explains the origin of species. When therefore we are told that health is natural, we may presume that what is meant is that it is normal; and that when we are told to pursue health as a natural end, what is implied is that the normal must be good. But is it so obvious that the natural must be good? Is it really obvious that health, for instance, is good? Was the excellence of Socrates or of Shakespeare normal? Was it not rather abnormal, extraordinary? It is, I think, obvious in the first place, that not all that is good is normal; that, on the contrary, the abnormal is often better than the normal: peculiar excellence, as well as peculiar viciousness, must obviously be not normal but abnormal. Yet it may be said that nevertheless the normal is good; and I myself am not prepared to dispute that health is good. What I contend is that this must not be taken to be obvious; that it must be regarded as an open question. To declare it to be obvious is to suggest the naturalistic fallacy: just as in some recent books, a proof that genius is diseased, abnormal, has been used to suggest that genius ought not to be encouraged. Such reasoning is fallacious, and dangerously fallacious. The fact is that in the very words health and disease we do commonly include the notion that the one is good and the other bad. But, when a so-called scientific definition of them is attempted, a definition in natural terms, the only one possible is that by way of normal and abnormal. Now, it is easy to prove that some things commonly thought excellent are abnormal; and it follows that they are diseased. But it does not follow, except by virtue of the naturalistic fallacy, that those things, commonly thought good, are therefore bad. All that has really been shewn is that in some cases there is a conflict between the common judgment that genius is good, and the common judgment that health is good. It is not sufficiently recognised that the latter judgment has not a whit more warrant for its truth than the former; that both are perfectly open questions. It may be true, indeed, that by healthy we do commonly imply good; but that only shews that when we so use the word, we do not mean the same thing by it as the thing which is meant in medical science. That health, when the word is used to denote something good, is good, goes no way at all to shew that health, when the word is used to denote something normal, is also good. We might as well say that, because bull denotes an Irish joke and also a certain animal, the joke and the animal must be the same thing. We must not, therefore, be frightened by the assertion that a thing is natural into the admission that it is good; good does not, by definition, mean anything that is natural; and it is therefore always an open question whether anything that is natural is good. (§ 27 ¶ 3)

But there is another slightly different sense in which the word natural is used with an implication that it denotes something good. This is when we speak of natural affections, or unnatural crimes and vices. Here the meaning seems to be, not so much that the action or feeling in question is normal or abnormal, as that it is necessary. It is in this connection that we are advised to imitate savages and beasts. Curious advice, certainly; but, of course, there may be something in it. I am not here concerned to enquire under what circumstances some of us might with advantage take a lesson from the cow. I have really no doubt that such exist. What I am concerned with is a certain kind of reason, which I think is sometimes used to support this doctrine—a naturalistic reason. The notion sometimes lying at the bottom of the minds of preachers of this gospel is that we cannot improve on nature. This notion is certainly true, in the sense that anything we can do, will be a natural product. But that is not what is meant by this phrase; nature is again used to mean a mere part of nature; only this time the part meant is not so much the normal as an arbitrary minimum of what is necessary for life. And when this minimum is recommended as natural—as the way of life to which Nature points her finger—then the naturalistic fallacy is used. Against this position I wish only to point out that though the performance of certain acts, not in themselves desirable, may be excused as necessary means to the preservation of life, that is no reason for praising them, or advising us to limit ourselves to those simple actions which are necessary, if it is possible for us to improve our condition even at the expense of of doing what is in this sense unnecessary. Nature does indeed set limits to what is possible; she does control the means we have at our disposal for obtaining what is good; and of this fact, practical Ethics, as we shall see later, must certainly take account: but when she is supposed to have a preference for what is necessary, what is necessary means only what is necessary to obtain a certain end, presupposed as the highest good; and what the highest good is Nature cannot determine. Why should we suppose that what is merely necessary to life is ipso facto better than what is necessary to the study of metaphysics, useless as that study may appear? It may be that life is only worth living, because it enables us to study metaphysics—is a necessary means thereto. The fallacy of this argument from nature has been discovered as long ago as Lucian. I was almost inclined to laugh, says Callicratidas, in one of the dialogues imputed to him, just now, when Charicles was praising irrational brutes and the savagery of the Scythians: in the heat of his argument he was almost repenting that he was born a Greek. What wonder if lions and bears and pigs do not act as I was proposing? That which reasoning would fairly lead a man to choose, cannot be had by creatures that do not reason, simply because they are so stupid. If Prometheus or some other god had given each of them the intelligence of a man, then they would not have lived in deserts and mountains nor fed on one another. They would have built temples just as we do, each would have lived in the centre of his family, and they would have formed a nation bound by mutual laws. Is it anything surprising that brutes, who have had the misfortune to be unable to obtain by forethought any of the goods with which reasoning provides us, should have missed love too? Lions do not love; but neither do they philosophise; bears do not love, but the reason is they do not know the sweets of friendship. It is only men, who, by their wisdom and knowledge, after many trials, have chosen what is best. (§ 28 ¶ 1)