physical Ethics’ in Chapter II. as based upon the naturalistic fallacy. To hold that from any proposition asserting ‘Reality is of this nature’ we can infer, or obtain confirmation for, any proposition asserting ‘This is good in itself’ is to commit the naturalistic fallacy. And that a knowledge of what is real supplies reasons for holding certain things to be good in themselves is either implied or expressly asserted by all those who define the Supreme Good in metaphysical terms. This contention is part of what is meant by saying that Ethics should be ‘based’ on Metaphysics. It is meant that some knowledge of supersensible reality is necessary as a premise for correct conclusions as to what ought to exist. This view is, for instance, plainly expressed in the following statements: ‘The truth is that the theory of Ethics which seems most satisfactory has a metaphysical basis. . . . If we rest our view of Ethics on the idea of the development of the ideal self or of the rational universe, the significance of this cannot be made fully apparent without a metaphysical examination of the nature of self; nor can its validity be established except by a discussion of the reality of the rational universe[1].’ The validity of an ethical conclusion about the nature of the ideal, it is here asserted, cannot be established except by considering the question whether that ideal is real. Such an assertion involves the naturalistic fallacy. It rests upon the failure to perceive that any truth which asserts ‘This is good in itself’ is quite unique in kind—that it cannot be reduced to any assertion about reality, and therefore must remain unaffected by any conclusions we may reach about the nature of reality. This confusion as to the unique nature of ethical truths is, I have said, involved in all those ethical theories which I have called metaphysical. It is plain that, but for some confusion of the sort, no-one would think it worth while even to describe the Supreme Good in metaphysical terms. If, for instance, we are told that the ideal consists in the realisation of the ‘true self,’ the very words suggest that the fact that the self in question is true is supposed to have some bearing on the fact that it is good. All the ethical truth
- ↑ Prof. J. S. Mackenzie, A Manual of Ethics, 4th ed., p. 431. The italics are mine.
