our ability by reflection to discover it, are the postulates of logic. It is for metaphysics to deal with both assumptions.
Yet we must never forget the dependence of ethics as a normative science upon the natural science of ethics. As we have just seen, the reflective formulation of morality is, like morality itself, progressive. It follows that the complete ethical formula at any stage must include all preceding formulae, and that the final ethical formula would be the last word of evolution itself. The true ethical interpretation of human life must be plastic as Aristotle's 'Lesbian rule,'—the living expression of the changing life of man; and the moral life does not, any more than the physical life, commit itself to any expression as final and exhaustive.
The normative sciences, however, are to be distinguished, no less than the natural sciences, from metaphysics or philosophy, whose province it is to deal with the question of the ultimate or absolute validity of all our judgments, whether they are judgments of fact or judgments of worth. Neither the natural nor the normative sciences deal with this question—the question of their own ultimate validity. It is the function of metaphysics to act as critic of the sciences; the sciences do not criticise themselves. Each assumes the validity of its own standpoint, and of its own system of judgment. The normative sciences deal with our judgments of worth, just as the natural sciences deal with our judgments of fact; neither the one group of sciences nor the other investigates the final validity of the judgments which, in their original chaotic condition, are the datum, and, in their systematic order, the result of the sciences in question. Whether natural or normative, science is content with the discovery of the unifying principle which organizes the several judgments of ordinary unscientific thought into a scientific system. The question of the grounds of our right to judge at all, whether about facts or values, and of the relative validity of our judgments of fact and our judgments of value, science leaves to metaphysics, which, in considering the epistemological question of the possibility of an ultimate vindication of human knowledge in general, is compelled to face the onto-
