None of the great thinkers, from Pythagoras down to Hegel, has left metaphysics where he found it. Yet none can be said to have built on the foundations of his predecessors in the same way as the mathematicians and physicists and chemists have added to the edifice they found. What the philosophers have done is to accumulate materials for the study of man’s faculties and modes of thinking, and of his ideas regarding his relations to the universe, while also indicating various methods by which the study may be pursued. Each great product of speculative thought is itself a part of these materials, and for that reason never becomes obsolete, as the treatises of the old physicists and chemists have mostly become. Aristotle, for instance, has left us books on natural history, on metaphysics and ethics, and on politics. Those on natural history are mere curiosities, and no modern biologist or zoologist needs them. Those on metaphysics and ethics still deserve the attention of the student of philosophy, though he may in a certain sense be said to have got beyond them. The treatise on politics still keeps its place beside Montesquieu, Burke, and Tocqueville. Or, to take a thinker who like Aristotle seems very far removed from us, though fifteen hundred years later in date, St. Thomas of Aquinum discusses questions from many of which the modern world has moved away, and discusses them by methods which many do not now use, starting from premises which many do not accept. But he marks a remarkable stage in the history of human thought, and as a part of that history, and as an example of extraordinary dialectical ingenuity and subtlety, he remains an object of interest to those least in agreement with his conclusions. [Sidenote: Every Great Thinker Affects Others] Every great thinker affects other thinkers, and propagates the impulse he has received, though perhaps in a quite different direction. The teaching of Socrates was the starting point for nearly all the subsequent schools of Greek philosophy. Hume became the point of departure for Kant, who desired to lay a deeper foundation for philosophy than that which Hume seemed to have overturned. All these great ones have not only enriched us, but are still capable of stimulating us. But they have not improved our capacity for original thinking. The accumulation of scientific knowledge has, as already observed, put all mankind in a better position for solving further physical problems and establishing a more complete dominion over Nature. The accumulation of philosophic thought has had no similar effect. In the former case each man stands, so to speak, on the shoulders of his predecessors. In the latter he stands on his own feet. The value of future contributions to philosophy will depend on the original power of the minds that make them, and only to a small extent (except by way of stimulus) on what such minds may have drawn from those into whose labours they have entered.