Ad hoc fallacies are explanations dressed up in lieu of argument or of valid explanation. The term is derived from the the Latin for "special purpose".
Both explanations and arguments serve important purposes, so it is vital to recognize fallacies of logic, misinformation and ad hoc rationalizations when determining the validity of an argument or explanation. Ad hoc pseudoexplanations may resemble valid explanations, but they lack the coherent logical or empirical support that validates legitimate explanations.
The difficulty with ad hoc pseudoexplanations arises in their misapplication for the sole purpose of supporting a favored hypothesis, particularly a hypotheses that lacks logical or empirical support. In this sense, ad hoc rationalizations are acts of desperation. These pseudoexplanations are essentially rabbits pulled from hats when confronted with inconvenient facts that threaten to refute one’s favoured belief or theory.
Ad hoc rationalizations employ arbitrary introduction of new, special-purpose elements into an argument in order to make the argument appear valid. These are probably elements that have convinced the arguer, who likely is emotionally committed to the conclusion to be drawn; sometimes for emotional reasons that are not immediately evident from the line of argument.
Ad hoc rationalizations, as distinct from legitimate explanations, are identifiable by several features: lack coherence, misapplied to single instances, run counter to accepted knowledge, explain nothing, and lack testable consequences.
Christian apologetics, indeed all religious apologetics, faced with utter lack of evidence or with counterevidence necessarily relies upon fallacies of logic and ad hoc pseudoexplanations. Some ad hoc apologist pseudoexplanations are very sophisticated indeed, reflecting the historic waste of great minds.
Probably the most familiar ad hoc rationalization is, "God works in mysterious ways."
Common ad hoc constructions take the forms:
● “Of course you do not see that I am right! As it says in [quote inserted], our [authority*] warns us that [preventer^] ensures that the wicked will refuse to see the Truth!”
● "Of course the [whoevers^^] did not see the [whatever**], [whatevers**] will not manifest to those who do not believe."
● "Of course the [whoevers^^] did not find evidence to support my viewpoint, they were biased by their [prejudice***]."
● "Of course the [whoevers^^] did not [action¨] the [whomever`], they were biased by their [prejudice***]."
^ insert 'Satan' (an all time favourite in such fallacious retorts), 'atheist', 'militant atheist' ("Quick get the gun, I see a Christian!"), 'liberal', 'Dawkins / Dennett / Harris /Hitchens', or, most ridiculous of all, 'science'.
^^ insert 'researcher', 'investigator', 'scientist', 'evolutionist', 'doctor', 'epidemiologist', 'expert', 'psychologist', etc.
* insert 'Bible', 'Scriptures', 'Jesus', 'church', 'priest', 'pastor', etc.** insert 'ghost', 'fairy', 'ESP', 'God', etc.
*** insert 'a priori assumption' (a misuse of 'a priori', incidentally), 'self-interest', 'self-protection', "brotherhood", 'prejudice', 'atheism', 'secularism', 'liberalism', 'environmentalism', 'socialism', 'cultism', 'Dawkinism,' 'Darwinism', 'greed' (always a big favorite with the conceptually challenged), etc.
¨ insert identities ("implied") 'creationist', "IDiot" ('intelligent design' creationist'), 'theist', 'apologist', 'religionist', 'fundamentalist', 'televangelist', 'bigot', 'racist', 'sexist', 'homophobe', etc.
` insert 'believe', 'agree with', 'hire', 'support'
We have all seen and heard variants of these fallacious pseudoarguments ad nauseam!