Bacon holds that philosophy has for its objects God, man, and nature, and he regards it as within his province to treat of “philosophia prima” (a sort of metaphysics, though he does not call it by this name), of logic, of physics and astronomy, of anthropology, in which he includes psychology, of ethics, and of politics.  In short, he attempts to map out the whole field of human knowledge, and to tell those who work in this corner of it or in that how they should set about their task.

As for Descartes, he writes of the trustworthiness of human knowledge, of the existence of God, of the existence of an external world, of the human soul and its nature, of mathematics, physics, cosmology, physiology, and, in short, of nearly everything discussed by the men of his day.  No man can accuse this extraordinary Frenchman of a lack of appreciation of the special sciences which were growing up.  No one in his time had a better right to be called a scientist in the modern sense of the term.  But it was not enough for him to be a mere mathematician, or even a worker in the physical sciences generally.  He must be all that has been mentioned above.

The conception of philosophy as of a something that embraces all departments of human knowledge has not wholly passed away even in our day.  I shall not dwell upon Spinoza (1632-1677), who believed it possible to deduce a world a priori with mathematical precision; upon Christian Wolff (1679-1754), who defined philosophy as the knowledge of the causes of what is or comes into being; upon Fichte (1762-1814), who believed that the philosopher, by mere thinking, could lay down the laws of all possible future experience; upon Schelling (1775-1854), who, without knowing anything worth mentioning about natural science, had the courage to develop a system of natural philosophy, and to condemn such investigators as Boyle and Newton; upon Hegel (1770-1831), who undertakes to construct the whole system of reality out of concepts, and who, with his immediate predecessors, brought philosophy for a while into more or less disrepute with men of a scientific turn of mind.  I shall come down quite to our own times, and consider a man whose conception of philosophy has had and still has a good deal of influence, especially with the general public—­with those to whom philosophy is a thing to be taken up in moments of leisure, and cannot be the serious pursuit of a life.

“Knowledge of the lowest kind,” says Herbert Spencer, “is un-unified knowledge; Science is partially-unified knowledge; Philosophy is completely-unified knowledge.” [1] Science, he argues, means merely the family of the Sciences—­stands for nothing more than the sum of knowledge formed of their contributions.  Philosophy is the fusion of these contributions into a whole; it is knowledge of the greatest generality.  In harmony with this notion Spencer produced a system of philosophy which includes the following:  A volume entitled