This foreshadows the doctrine of Bhûta-tathatâ and we seem to hear a prelude to the dialectic of Nâgârjuna when the Kathâvatthu discusses whether Suññatâ or the void is predicable of the Skandhas and when it condemns the views that anything now existing existed in the past: and that knowledge of the present is possible (whereas the moment anything is known it is really past). The Kathâvatthu also condemns the proposition that a Bodhisattva can be reborn in realms of woe or fall into error, and this proposition hints that the career of a Bodhisattva was considered of general interest. The Mahayana grows out of the Hinayana and in many respects the Hinayana passes into it and is preserved unchanged. It is true that in reading the Lotus we wonder how this marvellous cosmic vision can represent itself as the teaching of Gotama, but the Buddhacarita of Aśvaghosha, though embellished with literary mythology, hardly advances in doctrine beyond the Pali sutras describing the marvels of the Buddha's nativity[174] and the greater part of Nâgârjuna's Friendly Epistle, which purports to contain an epitome of the faith, is in phraseology as well as thought perfectly in harmony with the Pali Canon. Whence comes this difference of tone in works accepted by the same school? One difficulty of the historian who essays to account for the later phases of Buddhism is to apportion duly the influence of Indian and foreign elements. On the one hand, the Mahayana, whether we call it a development or perversion, is a product of Indian thought. To explain its trinities, its saviours, its doctrine of self sacrifice it is not necessary to seek abroad. New schools, anxious to claim continuity and antiquity, gladly retained as much of the old doctrine as they could. But on the other hand, Indian Buddhism came into contact with foreign, especially Iranian, ideas and undoubtedly assimilated some of them. From time to time I have drawn attention to such cases in this work, but as a rule the foreign ideas are so thoroughly mastered and indianized that they cease to be obvious. They merely open up to Indian thought a new path wherein it can move in its own way.