 Diels next posited that Theophrastus’ treatise, the Vetusta Placita, and Aëtius had the same kind of systematic lay-out as the extant Placita of ps-Plutarch, viz. according to subject. The individual books and sections of books of this tract are indeed concerned with specific themes, such as for instance book two, which deals with the cosmos and the heavenly bodies. Within the framework of a section devoted to a particular subject, e.g., the sun, or the moon, the individual chapters may be concerned with various specific issues pertaining to the sun, or the moon, and so on. 