Metaphysics, then, will have a bearing upon practical Ethics—upon the question what we ought to do—if it can tell us anything about the future consequences of our actions beyond what can be established by ordinary inductive reasoning. But the most characteristic metaphysical doctrines, those which profess to tell us not about the future but about the nature of an eternal reality, can either have no bearing upon this practical question or else must have a purely destructive bearing. For it is plain that what exists eternally cannot be affected by our actions; and only what is affected by our actions can have a bearing on their value as means. But the nature of an eternal reality either admits no inference as to the results of our actions, except in so far as it can also give us information about the future (and how it can do this is not plain), or else, if, as is usual, it is maintained to be the sole reality and the sole good, it shows that no results of our actions can have any value whatever.
69. But this bearing upon practical Ethics, such as it is, is not what is commonly meant when it is maintained that Ethics must be based on Metaphysics. It is not the assertion of this relation which I have taken to be characteristic of Metaphysical Ethics. What metaphysical writers commonly maintain is not merely that Metaphysics can help us to decide what the effects of our actions will be, but that it can tell us which among possible effects will be good and which will be bad. They profess that Metaphysics is a necessary basis for an answer to that other and primary ethical question: What ought to be? What is good in itself? That no truth about what is real can have any logical bearing upon the answer to this question has been proved in Chapter I. To suppose that it has, implies the naturalistic fallacy. All that remains for us to do is, therefore, to expose the main errors which seem to have lent plausibility to this fallacy in its metaphysical form. If we ask: What bearing can Metaphysics have upon the question, What is good? the only possible answer is: Obviously and absolutely none. We can only hope to enforce conviction that this answer is the only true one by answering the question: Why has it been supposed to have such a bearing? We shall find that metaphysical writers seem to have failed to distinguish this primary ethical question: What is good? from various other questions; and to point out these distinctions will serve to confirm the view that their profession to base Ethics on Metaphysics is solely due to confusion.
70. And, first of all, there is an ambiguity in the very question: What is good? to which it seems some influence must be attributed. The question may mean either: Which among existing things are good? or else: What sort of things are good, what are the things which, whether they are real or not, ought to be real? And of these two questions it is plain that to answer the first, we must know both the answer to the second and also the answer to the question: What is real? It asks us for a catalogue of all the good things in the Universe; and to answer it we must know both what things there are in the Universe and also which of them are good. Upon this question then our Metaphysics would have a bearing, if it can tell us what is real. It would help us to complete the list of things which are both real and good. But to make such a list is not the business of Ethics. So far as it enquires What is good? its business is finished when it has completed the list of things which ought to exist, whether they do exist or not. And if our Metaphysics is to have any bearing upon this part of the ethical problem, it must be because the fact that something is real gives a reason for thinking that it or something else is good, whether it be real or not. That any such fact can give any such reason is impossible; but it may be suspected that the contrary supposition has been encouraged by the failure to distinguish between the assertion “This is good,” when it means “This sort of thing is good,” or “This would be good, if it existed,” and the assertion “This existing thing is good.” The latter proposition obviously cannot be true, unless the thing exists; and hence the proof of the thing’s existence is a necessary step to its proof. Both propositions, however, in spite of this immense difference between them, are commonly expressed in the same terms. We use the same words, when we assert an ethical proposition about a subject that is actually real, and when we assert it about a subject considered as merely possible.
In this ambiguity of language we have, then, a possible source of error with regard to the bearing of truths that assert reality upon truths that assert goodness. And that this ambiguity is actually neglected by those metaphysical writers who profess that the Supreme Good consists in an eternal reality
