Aristotle, and W. Rhys Roberts. Rhetoric. Mineola, NY: Dover, 2004. Kindle Electronic Edition.
Book II, chapter 23.
Aristotle now begins to discuss ways of proving or disproving an argument. He begins by pointing out that opposites must be truly opposites for a proof to work. For example, “Temperence is beneficial; for licentiousness is hurtful” (Aristotle 2.23, B. 1397a). If in fact one part of the statement is false, the other likely is as well. A second proof would be by means of considering all possible meanings of key words. Because of semantic range, some arguments may be overturned. There are also some situations in which an action may not be appropriate or one can be shown to be appropriate based on the other. For instance, if it is not inappropriate for one person to pay taxes, it is all right to collect the taxes (Aristotle 2:23, B. 1397b). An a fortiori argument says that if the less likely condition is true the more likely one will be also (Aristotle 2.23, B. 1397b). Some arguments can work based on time. If an action was allowed at one time it may be expected at another time (Aristotle 2.23, B. 1398a). In a debate, if it is possible to get the opponent to admit to what he says is disallowed in you it is normally positive (Aristotle 2.23, B. 1398a). Defining terms carefully can lead to a successful argument based on the defined terms (Aristotle 2.23, B. 1398a). An inductive argument may also indicate that conditions were right for a certain argument (Aristotle 2.23, B. 1398b). An argument from precedent is often viable (Aristotle 2.23, B. 1399a). Refutation or proof of separate parts of an argument is also quite effective (Aristotle 2.23, B. 1399a). Consequences of an action may be used to indicate whether it is wise or not. Related to this idea, showing that similar results come from sinister causes is often effective (Aristotle 2.23, B. 1399b). Aristotle also endorses arguments based on motives, rather than fact (Aristotle 2.23, B. 1399b). Argument based on incredible events or contradictions may be easily refuted (Aristotle 2.23, B. 1400a). Comparing actions or past history often prove useful in argumentation (Aristotle 2.23, B. 1400b).