 The starting-point of Diels' (1879) inquiries was a hypothesis provided by his Bonn teacher and Doktorvater Hermann Usener (who had predecessors himself), concerning the identical or closely similar language used in reports of pre-Socratic and other philosophical doctrines contained in two late compendia, the Placita (‘Tenets’) surviving among our manuscripts of Plutarch, and the Eclogae of the anthologizer Stobaeus; this hypothesis Diels modified in certain respects, and also made much more complicated, as he attempted to trace back from ps-Plutarch and Stobaeus a long line of predecessors, each successively relied upon by later authors in compiling philosophers’ doctrines, all the way down to ps-Plutarch and Stobaeus themselves. In a truly magisterial way he gave it the aura of absolute certainty and unassailability which did much to ensure its dominating position in the study of ancient philosophy until today. The hypothesis may be briefly set out as follows.