eses; induction in philosophy, indeed, will preclude the use of hypotheses. It is the philosophical development, though, that on the whole interests M. de Roberty rather than the idea of a scientific metaphysic. Instead, he tells us, of admitting the immediate action of the whole of positive science on the conceptions of the world, the majority of modern thinkers hold that one mere minimal part of our knowledge — the theory of cognition — suffices to explain the march of the philosophical development. This results from the notorious imperfection of social studies. Intellectual evolution can never really be considered apart from the conditions which constitute what we call a society. Society draws from its own bosom the persistent causes of its own development and change. The hierarchy of conceptions which is actually evolved consists in the four orders of knowledge: knowledge scientific, knowledge philosophic, knowledge æsthetic, and knowledge practical or technical — science, philosophy, art, industry; into these four phases of evolution does intellectual evolution resolve itself. In this connection M. de Roberty sharply criticises Comte's law of the three stages of thought. M. de Roberty's notion of the end of philosophy being the union of finality and causality, is eminently suggestive as a description of the ultimate coincidence of abstract reflection and of scientific investigation which human knowledge ought to aim at. One wishes, though, that he had helped the reader more by making use, say, of the distinction between the form and the content of philosophy or of a philosophy. As to content, a philosophy can never be more than a systematization of the knowledge of a given epoch, but formally regarded philosophy ought to be able to lay down not an absolute system, but the outlines of such a system. One feels somehow that the author has not defined sharply enough the standard by which all philosophical development can be estimated as a thing in itself, even although no one would wish to separate that development from the general development of man or society by which it is influenced and which it influences. The book is a valuable contribution to the study of the thought of our time and evinces a masterly grasp and knowledge of philosophical problems and philosophical history.
The problem of perception offers three remarkable features from the point of view of the physicist, physiologist, and psychologist respectively. The first finds that the sequences of the non- material world of
