 In a nutshell, the function of a topos can be explained as follows. First of all, one has to select an apt topos for a given conclusion. The conclusion is either a thesis of the opponent that someone wishes to refute, or it is the assertion someone wishes to establish or defend. Accordingly, there are two uses of topoi: they can either prove or disprove a given sentence; some can be used for both purposes, others for only one of them. In Aristotle’s dialectic, most topoi are topic-neutral and need hence be selected by certain linguistic, semantic or logical features of the given conclusion; if, for example, the conclusion maintains a definition, one has to select a topos from a list of topoi pertaining to definitions, etc. Once the dialectician or rhetorician has selected a topos that is appropriate for a given conclusion, the topos can be used to construe a premise from which the given conclusion can be derived. If for example the argumentative scheme is ‘If a predicate is generally true of a genus, then the predicate is also true of any species of that genus’, we can derive the conclusion ‘the capacity of nutrition belongs to plants’ using the premise ‘the capacity of nutrition belongs to all living things’, since ‘living thing’ is the genus of the species ‘plants’. If the construed premise is accepted, either by the opponent in a dialectical debate or by the audience of a public speech, we can draw the intended conclusion. In the Rhetoric though the situation is slightly different (see below  § 7.4),  because here the topic-neutral type of topoi that was prevalent in the Topics seems to play a secondary role. Many topoi of the Rhetoric seem to be rather ‘material’ in the sense that they are only useful for establishing conclusions of a certain content; this is why the appropriate topos here cannot be selected by formal criteria, but must be chosen in accordance with the content of the envisaged conclusion—whether, for example, something is said to be useful or honourable or just, etc.