Analytical Approaches to the History of Zoroastrainism

There appears to be virtual agreements on the date of Zoroaster and on the fact that the religion of the Achaemenian dynasts is part of the history of Zoroastrianism. The subject which remains hotly debated is the reconstruction of a pre-Zoroastrian Iranian religion. The main problem in the study of Zoroastrian history is discontinuity between three distinct corpora of textual sources, namely: the Avesta, the Old Persian inscriptions and Zoroastrian literature, since none of them reflect the religion of the ordinary people.
In the academic discussions of the history of Zoroastrianism, three different approaches are observed: The first approach (fragmentizing) rejects the notion of a single Zoroastrian tradition and concentrates on the Gāthās as the only source of information for Zarathustra's teachings, and compares its notions and references with the Vedic tradition. The second approach (harmonizing) emphasizes on the combined evidence of Avesta and Pahlavi books. Its main attitude is the recognition of the fact that the three different collections basically reflect the teaching of Zarathustra and developments are not due to ruptures and breaks in the tradition or because of influence of other religions. The third approach (diversifying) regards the combined evidence of Avesta and Pahlavi books as a variegated elastic tradition rather than a strict doctrinal system, and describes the Mazdeism of Sasanian as an active efficient religion.