 The Epistles vary in length and their style is plain. There are, however, numerous ambiguities, due to language and vocabulary, often of Persian origin, and to mistakes in the transmission of the text. Bausani (1978, 11) thinks the authors were of Persian origin (cf. now Hamdani, Soufan 2019, 5). In general, however, the doctrines are fully and clearly exposed, with repetitions where necessary to the didactic function of the treatises.