 Aristotle denies (as we have seen) that the principles of a scientific demonstration are themselves to be reached by way of demonstration (APo. 72b19–20; 93b16–18). But a demonstration (sullogismos) is a strong form of argument, in which conclusions follow necessarily from the premises (APr. 24b18–20). So some weaker form of reasoning could be involved, such as “induction” in our modern sense: a generalization over a collection of particulars. The latter gives rise to the notorious “problem of induction” (sect. 4.2),  of which Aristotle shows some awareness (Top. 131b19–36): how can any limited range of observations justify a universal claim? But even leaving this aside, there is a serious objection to understanding Aristotle’s epagōgē in this way. The most such a generalization could show that all individuals of a certain class have certain characteristics (APo. 92a37–92b2): that all swans are white, for instance. It could not tell us that this characteristic is essential, one of the features that constitutes a swan as a swan. Aristotle also suggests that each of the principles of scientific explanation is in some sense self-evident: it “commands belief of itself” (kath’heautēn einai pistēn) (Top. 100b19–22). This seems to exclude the idea that these principles are reached by any process of reasoning. Epagōgē is, therefore, best regarded as “an immediate apprehension of essences or forms” (Harari 2004: 34) that occurs in the very process of perceiving particular individuals of a given kind.