We may, then, attribute the obstinate prejudice that a knowledge of supersensible reality is a necessary step to a knowledge of what is good in itself, partly to a failure to perceive that the subject of the latter judgment is not anything real as such, and partly to a failure to distinguish the cause of our perception of a truth from the reason why it is true. But these two causes will carry us only a very little way in our explanation of why Metaphysics should have been supposed to have a bearing upon Ethics. The first explanation which I have given would only account for the supposition that a thing's reality is a necessary condition for tis goodness. This supposition is, indeed, commonly made; we find it commonly presupposed that unless a thing can be shewn to be involved in the constitution of reality, it cannot be good. And it is, therefore, worthwhile to insist that this is not the case; that Metaphysics is not even necessary to furnish part of the basis of Ethics. But when metaphysicians talk of basing Ethics on Metaphysics they commonly mean much more than this. They commonly mean that Metaphysics is the sole basis of Ethics—that it furnishes not only one necessary condition but all the conditions necessary to prove that certain things are good. And this view may, at first sight, appear to be held in two different forms. It may be asserted that merely to prove a thing supersensibly real is sufficient to prove it good: that the truly real must, for that reason alone, be truly good. But more commonly it appears to be held that the real must be good because it possesses certain characters. And we may, I think, reduce the first kind of assertion to no more than this. When it is asserted that the real must be good, because it is real, it is commonly also held that this is only because, in order to be real, it must be of a certain kind. The reasoning by which it is thought that a metaphysical enquiry can give an ethical conclusion is of the following form. From a consideration of what it is to be real, we can infer that what is real must have certain supersensible properties: but to have those properties is identical with being good—it is the very meaning of the word: it follows therefore that what has these properties is good: and from a consideration of what it is to be real, we can again infer what it is that has these properties. It is plain that, if such reasoning were correct, any answer which could be given to the question What is good in itself? could be arrived at by a purely metaphysical discussion and by that alone. Just as, when Mill supposed that to be good meant to be desired, the question What is good? could be and must be answered solely by an empirical investigation of the question what was desired; so here, if to be good means to have some supersensible property, the ethical question can and must be answered by a metaphysical enquiry into the question, What has this property? What, then, remains to be done in order to destroy the plausibility of Metaphysical Ethics, is to express the chief errors which seem to have led metaphysicians to suppose that to be good means to possess some supersensible property. (§ 72 ¶ 1)