reality, by such sciences as psychology, sociology, or comparative philology, creates the same kind of naturalistic categories in the domain of the spirit. It is of nature in this sense that the idealist denies the real existence, since the time when Bishop Berkeley repudiated matter as a mere abstraction. And here again, the scientist comes to the support of the idealist with his keen awareness of the pragmatic character of his hypotheses on the ultimate physical constituents of reality. It is through this theory of the natural sciences that Croce succeeded in eliminating naturalistic transcendence from his thought, and, singularly enough, his first impulse in this direction came to him from his æsthetic studies, through his criticism of literary genres, of grammars, of the particular arts and of rhetorical forms. He saw how through them "nature" introduces itself, as a construction of the human spirit, in the pure spiritual world of art; and having denied its reality in art, he proceeded to discover it everywhere not as reality, but as an product of abstracting processes. This must not be interpreted as meaning that the naturalistic method is an illegitimate hybrid: it has its uses in its proper place, and not less in the study of mind than in the study of nature. It is only by mistaking its constructions or fictions for realities, that we can be tempted to deduce from the natural sciences a philosophy of nature, or from the applications of the naturalistic method to art and to the history of man, an æsthetics or a philosophy of history. But the natural sciences themselves are not responsible for the errors of philosophical naturalism. That such errors should not be limited exclusively to philosophers, but very often appear within the body of sciences like biology or psychology or sociology, is easily explained by the fact that no scientist is a pure scientist: but poor philosophy does not become science simply because it finds place in scientific books. The quarrel between vitalists and mechanicists, for one instance, is a philosophical (or historical), not a scientific dispute: and it reveals itself, ultimately, as the opposition not of conceivable realities, but merely of different methods in the elaboration of the historical datum. The coherent and clear-minded biologist is to-day a mechanicist, not because mechanism is the essence of reality, but because it is the postulate of his research. The vitalist, on the other hand, is inevitably brought by the trend of his thought to abandon science and to become more or less deliberately a philosopher. It is enough to mention in this connection such names as Driesch or Bergson.