 Usener’s influence is also the cause of a fatal blind spot in Diels. He failed to acknowledge that Theophrastus, too, had a sort of Doktorvater, namely Aristotle. Aristotle, in his treatises, as a rule lists and discusses the opinions (doxai) of men in general and of the experts (who often are philosophers) in particular, concerning an issue in metaphysics, or physics, or psychology, and sometimes ethics, before embarking on his own investigations. These opinions are ordered according to the method of diaeresis, or division: a classification according to sets, sub-sets and sub-sub-sets with specific differences. Aristotle checks to what extent these opinions are in agreement among themselves or contradict each other, and then tries to establish to what extent one of the available options may prove acceptable, at least as the starting-point for further inquiry, or whether some option may be available which others have failed to consider. We call these exegetical and evaluative overviews ‘dialectical’, in the Aristotelian sense of the word of course. An overview of this nature should establish which genus, or set, is at issue, that is to say whether we are faced with a theoretical discipline, such as physics (and then with what species, or sub-set, e.g., zoology), or with a non-theoretical discipline such as poetics. This approach should also be applied to the sub-sets, or particular objects of inquiry, embraced by a particular sub-set. According to Posterior Analytics 2.1 various aspects should (or may) be treated separately, viz.: (1) does the object of the inquiry possess a particular property or attribute, or not; (2) the reason why it does possess this attribute; (3) the existence or non-existence of the object (for instance: do gods exist?—a question one does not need to ask when humans, or the sun, are at issue); and (4), the substance or definition of the object. Here an important part is played by the Aristotelian so-called categories and other kinds of predicates, because it is of major importance to establish to what category (viz. substance, or quality, or quantity, or place, or doing and being-affected etc.) a given object of inquiry and/or its attributes belong, or whether and in what sense for instance motion (or rest) may be predicated of it. These four different primary questions, or types of questions, may moreover be formulated in respect of each category (viz., not only of substance, but also of quality, etc.). Take the objects of mathematics. According to Aristotle these do not belong to the category of substance but to that of quantity. But within this latter category one may formulate questions about properties, or attributes, which may belong to them; enquire whether they exist, and if so, in what way; ask whether they move or not; and so on.