THREE:Finally, by the form which he gave to Platonism, Plotinus has had a large share in determining the direction of modern metaphysics. Although, as we have seen, not, properly speaking, a pantheist himself, he showed how the ideal theory could be transformed into a pantheistic system, and pantheism it immediately became when the peculiar limitations and subtleties of Greek thought had ceased to dominate over the western mind, and when the restraints of Catholic orthodoxy had been removed or relaxed. The stream of tendency in this direction runs all through the Middle Ages, and acquires new volume and momentum at the Renaissance, until, by a process which will be analysed in the next chapter, it reaches its supreme expansion in the philosophy of Spinoza. Then, after a long pause, it is taken up by Kants successors, and combined with the subjective idealism of modern psychology, finally passing, through the intervention of Victor Cousin and Sir William Hamilton, into the philosophy of Mr. Herbert Spencer.Whether Spinoza ever read Plato is doubtful. One hardly sees why he should have neglected a writer whose works were easily accessible, and at that time very popular with thinking minds. But whether he was acquainted with the Dialogues at first hand or not, Plato will help us to understand Spinoza, for it was through the door of geometry that he entered philosophy, and under the guidance of one who was saturated with the Platonic spirit; so far as Christianity influenced him, it was through elements derived from Plato; and his metaphysical method was one which, more than any other, would have been welcomed with delight by the author of the Meno and the Republic, as an attempt to realise his own dialectical ideal. For Spinozism is, on the face of it, an application of geometrical reasoning to philosophy, and especially to ethics. It is also an attempt to prove transcendentally what geometricians only assumethe necessity of space. Now, Plato looked on geometrical demonstration as the great type of certainty, the scientific completion of what Socrates had begun by his interrogative method, the one means of carrying irrefragable conviction into every department of knowledge, and more particularly into the study of our highest good. On the other hand, he saw that geometricians assume what itself requires to be demonstrated; and he confidently expected that the deficiency would be supplied by his own projected method of transcendent dialectics. Such at least seems to be the drift of the following passage: