The term doxographer is used to describe ancient authors who wrote summaries, or compilations of the opinions of earlier philosophers. Aristotle was the first to systematically collect opinions of his predecessors, and his work was further extended by his successor, Theophrastus. Several later writers wrote on the lives and opinions of the philosophers and provide extremely valuable resources for understanding the works of those whose writings are no longer extant. One cannot accept the works of the doxographers uncritically, as they often were working from inaccurate sources or were more intent on working out a system (of philosophical successions or of typology of rideas)than in unbiased reporting in the modern sense.

In the first or second century C.E., Aetius wrote an extensive summary of the works of earlier thinkers on natural philosophy. His work is preserved by subsequent writers and provides a...