First a few words about the distinction of periods in general. Among unreflecting people, for centuries, it has been customary to settle disputes by appeals to the Bible as a whole. This was always satisfactory, until somebody else came along who held totally different views, which he supported just as satisfactorily from the same authority. The result was the century-long bloody wars of the Reformation, everywhere leaving in that particular place, as the orthodox, the stronger. Since thirty years, however, the situation has changed. The contradictions of the Bible, so long the ammunition of scoffers of the type of Ingersoll, became the pathfinders of the Higher Criticism, which has solved the otherwise insoluble difficulties by showing them to rest on parallel documents, and different authors. It is no longer sufficient to appeal to Isaiah; we must now specify which Isaiah we mean; and we may no longer refer to the book of Genesis, but to the Jehovistic or Elohistic documents. This method of criticism is slowly gaining ground with other works. The writer, for instance, applied it with success to the Gathas, or hymns of Zoroaster. These appear in the Yasnas in two sections which have ever given the editors much trouble. Either they were printed in the meaningless traditional order, or they were mixed confusedly according to the editor's fancy, resulting of course in a fancy picture. The writer, however, discovered they were duplicate lives of Zoroaster, and printing them on opposite pages, he has shown parallel development, reducing the age-long difficulties to perfectly reasonable, and mutually confirming order. Another case is that of Plato. It is still considered allowable to quote the authority of Plato, as such; but in scientific matters we must always state which period of Plato's activities, the Plato of the Republic, or the more conservative Plato of the Laws, and the evil World-soul, is meant. Another philosopher in the same case is Schelling, among whose views the text-books distinguish as many as five different periods. This is no indication of mental instability, but rather a proof that he remained awake as long as he lived. No man can indeed continue to think with genuineness without changing his views; and only men as great as Bacon or Emerson have had the temerity to discredit consistency when it is no more than mental inertia. There are many other famous men who changed their views. Prominent among them is Goethe, whose Second Faust, finished in old age, strongly contrasted with the First Part. What then would be inherently unlikely in Plotinos's changing his views during the course of half a century of philosophical activity? On the contrary, it would be a much greater marvel had he not done so; and the burden of proof really lies with the partisans of unchanging opinions.