Dictionary of Fallacies
[A B C D E F G H I J K L M N O P Q R S T U V W X Y Z]
(Note that, for the sake of not having a rather bloated “A” section, the “argumentum ad” part of fallacy names is not considered in alphabeticization.)
A
Affirming the Consequent
In a modus ponens syllogism, this is the fallacy of affirming the consequent rather than antecedent term in the first premise. This means that, instead of “if p then q, p, therefore q” the argument takes the form “if p then q, q, therefore p”. See also: denying the antecedent.
Examples:
(1) If a person is a politician, they must be greedy, and Bob is greedy. Therefore, Bob must be a politician.
(2) When an earthquake occurs, there are always fires. There is a fire downtown right now, so there must have just been an earthquake.
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B
Begging the Question
Also known by its Latin name, petitio principii. This is an informal fallacy of circular reasoning, wherein the conclusion of an argument is also a (usually implicit) premise. Such arguments take the form “p, therefore p”, which is why they are said to beg the question — i.e., the truth of the conclusion becomes conditional on its own truth, which then begs the question of whether it is, in fact, true.
Examples:
(1) I know the Bible is true, because it says it is. (one has to assume it is true before the premise has any meaning)
(2) It’s obvious that God exists, because the Bible says He does, and the Bible — as the Word of God — can’t be wrong. (requires assuming that the Bible is the Word of God, which, of course, can only be true if God exists)
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C
Category Mistake
A category mistake occurs whenever one refers to one thing or concept in the context of an altogether different category of things/concepts. A more specialized version of this fallacy is reification.
Examples:
(1) The Theory of Evolution hinges on the survival of the fittest. Therefore, the only morality an evolutionist can have is “strength is good”. (the theory of evolution is a scientific theory, not a moral theory)
(2) You claim that murder is morally wrong. But if morality were really true, that would mean it would be impossible to commit murders. Yet murders really can and do happen, so, therefore, morality is just an illusion. (this mistakes morality for a law of nature — i.e., what sort of things can be done — as opposed to a statement about what sort of things ought to be done)
Complex Question
The informal fallacy of trying to implicitly settle a contentious issue by wording another question so as to assume it.
Examples:
(1) Have you stopped beating your wife yet? (tries to trick the asker into implicitly agreeing that he beats his wife)
(2) You deny having stolen any money, but I have to ask: is the amount you stole greater than $100? (same idea)
Composition
Also known as the salesman’s fallacy, this is the error of assuming that a whole must have/lack some property because its parts have/don’t have it. In reality, a whole may have properties very different from its individual parts.
Examples:
(1) All of the payments towards this new car are very small; therefore, the price of the car is very small. (naturally, the size of individual payments does not affect the size of the entire payment)
(2) An individual brain cell does not have any measure of consciousness. Therefore, consciousness cannot exist as a physical property of the brain. (the fact that any one brain cell lacks consciousness does not mean that the brain as a whole lacks it)
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D
Denying the Antecedent
In a modus tollens syllogism, the fallacy of denying the antecedent rather than consequent term in the first premise. This means that, instead of “if p then q, not-q, therefore not-p” the argument takes the form “if p then q, not-p, therefore not-q”. See also: affirming the consequent.
Examples:
(1) If it’s pouring then it’s raining, but it’s not pouring. Therefore, it’s not raining.
(2) Whenever she’s depressed she wants to go to the pub. She’s not depressed, therefore she won’t want to go to the pub.
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E
Equivocation
This is a matter of using an ambiguous word with the purpose of exploiting that ambiguity — that is, using a single word to refer to disparate concepts, and hence attempt to illictly equate those concepts. Despite what that wording suggests, most equivocation is actually done quite unintentionally.
Examples:
(1) All laws must have a lawgiver. Therefore, the Law of Gravity has a lawgiver. (equivocates between two different senses of the word “law”)
(2) A theory is just a guess, so the Theory of Evolution must be merely a baseless supposition. (equivocates between a colloquial usage of the word “theory” and the scientific usage of the term)
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F
False Analogy
Really a more specialized sort of straw man fallacy, this is a matter of trying to characterize a position by means of an inaccurate analogy, then making one’s argument with reference to that analogy, and finally concluding that the original position is true.
Example:
You say evolution is a plausible explanation for life reaching its current state. But the idea of a bunch of boards and nails sitting on the ground spontaneously forming into a house is, of course, ridiculously improbable. And this is precisely what evolution proposes. (evolution deals with organisms, so likening it to inanimate objects assembling themselves is completely misleading)
False Disjunction
Also called false bifurcation or false dilemma. This is the fallacy of trying to establish a conclusion by means of a disjunctive syllogism when, in fact, the complete range of logically possible choices are not addressed. In other words, this is trying to limit the discussion to a certain number of possible choices when in fact more choices are possible.
Examples:
(1) Jesus was either the Lord, a liar, or a lunatic. It’s impossible that Jesus could be a liar or a lunatic, therefore he is the Lord. (Jesus could also be “mistaken” or “misquoted” just to name two, making the disjunctive argument invalid)
(2) Either Yahweh exists, or there is no God. (ignores the possibility that a God other than Yahweh might exist)
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H
ad Hominem
This is perhaps the most misunderstood of all fallacies. Some understand it to refer merely to the practice of insulting or deriding a debate opponent, so that any wisecrack or disparaging remark is labelled a “fallacy”. In fact, however, mere derision only qualifies as rhetoric, not the formal ad hominem fallacy. For the fallacy to apply, a person must attempt to use a personal attack to actually disprove an argument.
Examples:
(1) Bob is arguing that Elvis is alive, when all the evidence clearly indicates his death. What a gibbering simpleton! (ad hominem rhetoric, but not the logical fallacy)
(2) Since Bob is nothing but a gibbering simpleton, his argument for the existence of Elvis must be incorrect. (the formal ad hominem fallacy)
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I
ad Ignorantiam
Literally, “argument to ignorance”. This is the fallacy of asserting that a proposition, since not proven true, is false; or, alternatively, true since it is not proven false. In fact, lack of evidence for or against a proposition only offers justification for the claim that one ought to suspend judgment on the matter.
Examples:
(1) Nobody can prove God doesn’t exist, so therefore He clearly does.
(2) Nobody can prove a God exists, so therefore no Gods exist.
(3) If you can’t prove me wrong, I must be right.
Ignoratio Elenchi
A fallacy of arguing to a conclusion which may appear to have some bearing on the current issue, but in fact does not.
Examples:
(1) Some claim that capital punishment is a deterrent to crime. Studies show, however, that prison employees involved with executions often suffer very grievous mental difficulties afterwards, and the cost of executions is extremely high — so, really, capital punishment just isn’t worth it. (regardless of whether those points are valid, they say nothing about whether capital punishment is a deterrent to crime)
(2) You claim that atheism is true, but atheists throughout history have been extremely evil individuals with no regard for human life. (again, regardless of whether those accusations are correct, they have no bearing on the claim that atheism is true)
Incredulity, argument from
This is a matter of denying something on the basis that it seems “just impossible” to you. This argument essentially involves saying “I cannot see how X would be true”; however, personal incredulity alone does not falsify a proposition. In order to falsify a proposition it must actually be demonstrated to be impossible.
Examples:
(1) I can’t believe that something as complex as the eye could evolve without help from a Designer. So, non-theistic conceptions of evolution cannot account for the complexity of the eye.
(2) I can’t conceive of a God who would design a universe full of natural evil, so clearly no God designed this universe.
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N
Non Sequitur
“It does not follow”. This is a label that can, really, be applied to any formal fallacy. It is, however, usually used to denote arguments which don’t even really have any appearance of correct logic.
Examples:
(1) The sky is blue, and coffee is grown in Brazil. Therefore, renegade squirrels are plotting the destruction of all mankind.
(2) I tell you, man, them Canadians are way too quiet up there… and they’re too damned polite. They’re going to up and invade any day now, mark my words.
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P
Petitio Principii
See begging the question.
ad Populum
The fallacy of concluding that, because the majority of people accept a proposition, the proposition is true. There is a non-fallacious sense of ad populum, but it only applies when the majority opinion actually does have some direct bearing on the issue.
Examples:
(1) Over 80% of the population believes in some sort of God, so atheism is probably false. (the ad populum fallacy)
(2) Over 80% of the population can’t tell Whizzo Butter from a dead crab. Therefore, Whizzo really tastes like a dead crab to most people. (a Monty Python reference, but not a fallacy)
Post Hoc Ergo Propter Hoc
Literally, “after the fact, therefore because of it.” This is the fallacy of assuming that correlation demonstrates causation.
Examples:
(1) I stepped on a spider, and it rained the next day. So, stepping on a spider must cause rain.
(2) Bob had a bad headache, so we prayed for him, and the next day he felt much better. So, prayer must have the power to cure.
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R
Reification
This term means “treating as a thing”. Reification is hence fallacious when an emotion, concept, or similar notion is treated as an object. See also: category mistake.
Examples:
(1) You say love exists, but where does it exist? There is no physical substance called “love”, so you must be mistaken. (love is not a “thing”, but at emotion, so asking “where does it exist” is irrelevant and misleading)
(2) It is obvious that numbers exist, for otherwise we could not count anything. But we cannot see, taste, or touch a number. Therefore, numbers must exist in a nonphysical realm. (numbers are concepts, not objects, and hence don’t have to exist as things at all)
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S
Special Pleading
This is a matter of trying to negate or ignore an argument on the basis of some kind of overarching concern. In fact, regardless of the validity of any such concerns, they have no bearing on the actual truth of an argument. The point here can be summed up thus: “sometimes, the truth hurts”. Some specialized versions of special pleading are: argumentum ad misericordiam, or the appeal to pity, and argumentum ad baculum, or the appeal to force/intimidation.
Examples:
(1) Your argument concludes that God cannot exist. But if you prove that to everyone, former theists won’t have any reason to be moral. So, your claims must be considered false. (special pleading)
(2) If you manage to prove that God exists, a lot of people will think they are going to hell. That’s a terrible thing to do to those poor people, so we should ignore such arguments. (ad misericordiam)
(3) Sure, you could try to prove that there was good evidence for God existing or not existing. But then I’d have to send some of my friends from the League of Agnostics around to break your kneecaps. (ad baculum)
Straw Man
This is a matter of setting up a weaker version of an opposing argument, attacking that version, and then claiming to have refuted the original argument.
Examples:
(1) Bob says that women tend, on the average, to be physically weaker than men. But women are not inferior to men, and are just as capable of contributing to society! (note that Bob never claimed women were inferior, or incapable of contributing to society)
(2) You claim that no civilized society practices capital punishment. So, I suppose you think it’s “civilized” just to let criminals run around free and unpunished? (not practicing capital punishment does not mean letting criminals run free)
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T
Tu Quoque
Literally, “you too”. This is the fallacy of trying to deny or negate an accusation by making a reciprocal accusation. This is a fallacy simply because such an “oh yeah, well you too” response, even if actually true, doesn’t make the original accusation any less true. It should be noted that there is a non-fallacious sense of tu quoque as well — when the argument actually applies to matters of character.
Examples:
(1) You claim that the evidence suggests I embezzled funds. But you, sir, have engaged in a number of extramarital affairs, so you are hardly in the position to be levelling any accusations. (the tu quoque fallacy)
(2) You claim to have caught me embezzling funds. But given that you yourself are known to be a pathological liar, I hardly think your testimony can be considered convincing. (not a fallacy, because here the “you too” is directly relevant)
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V
ad Verecundiam
This is the fallacious appeal to authority. Appeals to authority in general are rarely compelling, but this fallacy specifically refers to appeals to “authorities” who do not actually have any specific authority on the subject in question.
Examples:
(1) Mozart believed in God. If a great man like that is a theist, how can we disagree? (Mozart was certainly a great composer, but that doesn’t denote any expertise in philosophy)
(2) Douglas Adams is an atheist. If a writer and humourist of such intelligence is an unbeliever, I feel quite justified in my unbelief. (being a brilliant writer and humourist similarly denotes no knowledge about the existence of God)