Aristotle introduces four common lines of argument (or topoi, singular topos, in Greek) found in all three branches of oratory: possibility (most useful for deliberative); past fact (most useful for forensic); future possibility (also useful for deliberative); and magnitude, or the relative greatness of things (most useful for epideictic). These topoi form a store of general knowledge that a speaker can use to construct an argument.

Beginning with the Possible and Impossible, Aristotle establishes that there are various conditions which make things possible; for example, one might consider whether a given event has a necessary antecedent. In determining whether something is impossible, the speaker should make the opposite considerations.

Regarding Past Fact, Aristotle suggests a number of ways to determine whether an event has occurred, for example: “[I]f the less probable of two things has occurred, the more probable should have occurred as well” (145). Future Fact operates on the same principles as Past Fact, but transposed to the likelihood of future events. Finally, Aristotle advises magnifying or diminishing events in comparison with other events as needed.

He now moves on to three more universal topoi: Example; Maxim; and Enthymeme. Aristotle in fact argues that maxim is more appropriately a category of enthymeme, but he still discusses maxims at some length.