Nevertheless, by dint of pertinacious repetition, the founder of Neo-Platonism has succeeded in making the main outlines, and to a great extent the details, of his system so perfectly clear that probably no philosophy is now better understood than his. In this respect, Plotinus offers a remarkable contrast to the two great thinkers from whom his ideas are principally derived. While Plato and Aristotle construct each particular sentence with masterly clearness, the general drift of their speculations is by no means easy to ascertain; and, even now, critics take diametrically opposite views of the interpretation which is to be put on their teaching with regard to several most important points. The expositors of Neo-Platonism, on the contrary, show a rare unanimity in their accounts of its constitutive principles. What they differ about is its origin and its historical significance. And these are points on which we too shall have to enter, since all the ancient systems are interesting to us chiefly as historical phenomena, and Neo-Platonism more so than any other. Plotinus effected a vast revolution in speculative opinion, but he effected it by seizing on the thoughts of others rather than by any new thoughts or even new developments or applications of his own. Whether Plotinus was or was not the disciple of Ammonius, it is beyond all doubt that he considered himself the disciple of Plato. There are more than a hundred references to that philosopher in the _Enneads_, against less than thirty references to all the other ancient thinkers put together;[428] and, what is more remarkable, in only about half of them is he mentioned by name. The reader is expected to know that ‘he’ always means Plato. And it is an article of faith with Plotinus that his master cannot be mistaken; when the words of oracular wisdom seem to contradict one another, there must be some way of harmonising them. When they contradict what he teaches himself, the difficulty must be removed by skilful interpretation; or, better still, it must be discreetly ignored.[429] On the other hand, when a principle is palpably borrowed from Aristotle, not only is its derivation unacknowledged, but we are given to understand by implication that it belongs to the system which Aristotle was at most pains to controvert.[430]