[Note: This is the 3rd entry in the How Not to Argue series. See also Heuristics and Hyperbole and No True Scientist.]
Although an argument free of fallacies is not always good, a good argument is always free of fallacies.
While that chiastic assertion may not be completely true (or even fallacy-free) it is a fair summation of the fallacy theory of T. Edward Damer, philosopher and author of Attacking Faulty Reasoning. According to Damer, a fallacy is a violation of one of the five criteria of a good argument:
- the argument must be structurally well-formed,
- the premises must be relevant,
- the premises must be acceptable,
- the premises must be sufficient in number, weight, and kind, and
- there must be an effective rebuttal of challenges to the argument.
Spotting fallacies in your own argument is one of the easiest ways to ensure they are more persuasive. Unfortunately, it can be difficult to keep track of the endless list of informal fallacies and their Latin nomenclature (ad argumentum ad infinitum). A useful heuristic is to instead become familiar with Damer’s five fallacy categories and the most common fallacies within each:
Fallacies that violate the structural criterion — The structural criterion requires that one who argues for or against a position should use an argument that meets the fundamental structural requirements of a well-formed argument, using premises that are compatible with one another, that do not contradict the conclusion, that do not assume the truth of the conclusion, and that are not involved in any faulty deductive inference.
Begging the Question (petition principii) — The truth of the conclusion is assumed by the premises. Often, the conclusion is simply restated in the premises in a slightly different form. In more difficult cases, the premise is a consequence of the conclusion.
Example: “We know that God exists, since the Bible says God exists. What the Bible says must be true, since God wrote it and God never lies.” (Here, we must agree that God exists in order to believe that God wrote the Bible.))
Undistributed Middle — The middle term in the premises of a standard form categorical syllogism never refers to all of the members of the category it describes.
Example:“All Baptists are Christians, and all Catholics are Christians, therefore, all Baptists are Catholics.”
The middle term is ‘Christians’. While both Baptist and Catholics share the common property of being Christians, they may be separate groups of Christians, and so we cannot conclude that Baptists are otherwise the same as Catholics in any way.
Denying the antecedent — a logical fallacy that takes the form:
If P, then Q.
Therefore, not Q.
If Joe is a Catholic, then he is a human being.
Joe is not a Catholic.
Therefore, Joe is not a human being.
Fallacies that violate the relevance criterion — The relevance criterion requires that one who presents an argument for or against a position should attempt to set forth only reasons that are directly related to the merit of the position at issue.
Argumentum ad baculum — is an argument where force, coercion, or the threat of force, is given as a justification for a conclusion.
Example: “You should believe in the God of the Bible, because if you do not and you die, you will go to hell.”
Appeal to tradition — a fallacy in which the conclusion is deemed to be correct because it adheres to a long standing tradition.
Example: “America has historically been a Christian nation; therefore we should not allow Hindus to lead prayer in the Senate.”
Genetic fallacy — a conclusion is suggested based solely on something or someone’s origin rather than its current meaning or context.
Damer gives the following example: “”You’re not going to wear a wedding ring, are you? Don’t you know that the wedding ring originally symbolized ankle chains worn by women to prevent them from running away from their husbands? I would not have thought you would be a party to such a sexist practice.” There may be reasons why people may not wish to wear wedding rings, but it would be logically inappropriate for a couple to reject the notion of exchanging wedding rings on the sole grounds of its alleged sexist origins.” (p. 36)
Fallacies that violate the acceptability criterion — The acceptability criterion requires that one who presents an argument for or against a position should attempt to use reasons that are likely to be accepted by a rationally mature person and that meet the standard criteria of acceptability.
Equivocation – the same word is used with two different meanings.
Example: “Criminal actions are illegal, and all murder trials are criminal actions, thus all murder trials are illegal.” (Here the term “criminal actions” is used with two different meanings.)
Fallacy of division — an inference that what is true of a whole must also be true of its constituents and justification for that inference is not provided.
Example: “A living cell is organic material, so the chemicals making up the cell must also be organic material.”
Fallacies that violate the sufficiency criterion — The sufficiency criterion requires that one who presents an argument for or against a position should attempt to provide reasons that are sufficient in number, kind, and weight to support the acceptance of the conclusion.
Argumentum ad ignorantiam (argument from ignorance) – arguments of this form assume that since something has not been proven false, it is therefore true. Conversely, such an argument may assume that since something has not been proven true, it is therefore false. (This is a special case of a false dilemma, since it assumes that all propositions must either be known to be true or known to be false.)
Example: “Since Christians cannot prove that Jesus existed, we should assume that he probably didn’t.”
Special Pleading — a fallacy in which a person applies standards, principles, rules, etc. to others while taking herself (or those she has a special interest in) to be exempt, without providing adequate justification for the exemption.
Example: “As a man, you naturally don’t understand the arguments supporting abortion.”
Fallacies that violate the rebuttal criterion — The rebuttal criterion requires that one who presents an argument for or against a position should attempt to provide an effective rebuttal to all serious challenges to the argument or the position it supports and to the strongest arguments for viable alternative positions.
Straw Man – The author attacks an argument which is different from, and usually weaker than, the opposition’s best argument.
Example: “We should reinstate military conscription. People don’t want to enter the military because they find it an inconvenience. But they should realize that there are more important things than convenience.”
Poisoning the well — a logical fallacy where adverse information about someone is preemptively presented to an audience, with the intention of discrediting or ridiculing everything that person is about to say. (Poisoning the well is a special case of argumentum ad hominem.)
Example: “You can’t trust anything Joe Carter says — he’s a blogger.”