The fallacy of ignoratio elenchi (“ignorance of the argument”) comes in many forms. The traditional species are marked by a Latin nomenclature: the ad hominem (“to the man”), ad baculum (“to force”), ad misericordiam (“to pity”), ad populum (“to the people”) and ad verecundiam (“to reverence” or “authority”).[note]
Ignoratio elenchi means, literally, “ignorance of refutation”. The term arises as a Latin translation of Aristotle’s name for one of the thirteen fallacies he describes in De Sophisticis Elenchis, and has covered a wide range of logical sins since. For example, C.L. Hamblin, Fallacies (New York: Methuen, 1970) pp. 41 ff, lists fully 24 species of this fallacy and Alex Michalos, Improving Your Reasoning (Englewood Cliffs, J.: Prentice-Hall, 1970), pp. 50-67, lists 21. (I am indebted to David Hitchcock here.) All such noted species of the ignoratio elenchi, however, conform to the unifying principle we cite.[/note] The common principle underlying these and all other types of the ignoratio elenchi is that each diverts the argument onto a premise that is irrelevant to the claim in contention. Because they are familiar and recognizable kinds of dishonest argumentation – in particular, the appeals ad hominem and ad baculum which are a stock-in-trade of everyday communication and exchange – they are widely enshrined as fallacies in informal logic courses and texts. Indeed knowledge of the ad hominem has achieved such wide currency that it has passed into the language as a more or less standard term of literate discourse.
What I wish to propose here is that there is a kind of ignoratio elenchi so far unrecognized which is as easily identifiable and more influentially misleading than the traditional types, but which has as yet escaped a name to detect it. This kind, as all others of its species, diverts argument onto an irrelevant premise, but it does so in a special way: by rerouting discussion onto the alleged property or behaviour of a common adversary.[note]
We use the phrases “common adversary”, “conventional foe”, ”customarily shared opponent” and so on interchangeably. What qualifies a party or entity, E, for the status referred to by these and similar expressions is that the social group, G, within whose context E is invoked, has as a group a predictable tendency to attack It is consistent with this description that some individual members of G, whether G is a national television audience or a living room gathering, may as individuals dissent from G’s disposition to attack E. (It would be a fallacy of division to infer the contrary.) It also follows that in some cases, say, “big unions”, “women’s libbers”, or “student radicals”, G’s collective reaction to invocation of these as E, will vary from G to G, depending on the composition of the group appealed to. (The “common adversary” here will be predictable for some groups, business or conservative, but not predictable for others.) It is these complicating factors that can account for cases of the ad adversarium’s dramatic failure (e.g. hisses from the audience), or change of adversarial objects over time with the same group.[/note]