 The Aëtius hypothesis was new; it has proved to be tenable, though it has been shown to be in need of revision. Before Diels, scholars believed in the existence of a single early source, parts of which would have been taken over and adapted by Cicero as well as much later by, for instance, ps-Galen. The Vetusta Placita hypothesis, on the other hand, is dubious, and the way back to Theophrastus is much more complicated and uncertain, if only because hard evidence is so scarce, than Diels, who just stuck to Usener’s point of view about Theophrastus, wished to consider. 