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So, acceptability of evidence and relevance and sufficiency of the link between evidence and claim constitute the standards for assessing the quality of an argument. Those standards do not suggest that the argument is either perfect or completely disqualified. The standards place the argument along a continuum somewhere between very good and very poor.
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Those standards for the quality of argument are useful for assessing whether an argument is relatively good or relatively poor. A specific application of the standards has to do with a concept called “fallacy.” A fallacy is an error in reasoning and has a negative effect on the assessment of an argument’s quality. In the next section, fallacies will be identified that are directly related to the standards of quality presented herein.
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21.2 Three Basic Fallacies
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The presence or absence of fallacies is a good general method for placing arguments along the continuum of very good to very poor. The absence of fallacies does not guarantee that the argument is a good one, nor does the presence of a fallacy automatically disqualify an argument from consideration. Fallacies invite, perhaps require, the arguer to improve the argument in order to make it more persuasive. In other words, the presence or absence of fallacies does not automatically mean people should or should not give consideration to the argument. The presence of one or more fallacies does, however, direct a listener to give more critical attention to the claim.
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The system used in this text, abstracted from the Johnson and Blair Model of Argument Cogency, includes three basic fallacies, one corresponding to each of Johnson and Blair’s three criteria for a logically adequate argument. The basic fallacies include the problematic premise, the irrelevant reason, and the hasty conclusion. Problematic premises are problems with the acceptability of evidence. Irrelevant reasons involve a lack of relationship between evidence and claim, and hasty conclusions indicate that the relationship between evidence and claim is insufficient.
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Although each fallacy has been placed in a particular category, some of the fallacies can logically fall into more than one category. That system of categorization is intended only to illustrate the basic categories of fallacies. No claim to a broader theory including a master taxonomy is made.
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21.2.1 Problematic Premises
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A problematic premise refers to an argument that, for some reason, fails to fulfill the acceptability requirement. In that case, unacceptable evidence usually results in a claim that is unsuccessful at gaining the support of the audience or the judge.
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A premise is not problematic if it meets any one of the three acceptability requirements discussed earlier. Evidence can be problematic when a debater needs to, but does not, provide further support for the evidence.
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For instance, a debater might argue against the use of airbags and seatbelts by using the evidence that when those devices were introduced in the United States, they had no positive effect on the number of automobile accidents or on the number of deaths associated with those accidents. Such evidence might not be accepted because it is not common knowledge and was not supported by a cogent sub argument or a respectable source or authority.
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So, problematic premises are about evidence. Two variants on problematic premises are discussed below.
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21.2.1.1 Begging the Question Begging the question is a fallacy that occurs in an argument when the evidence is essentially the same as the claim. Because the evidence and the claim are the same, the argument essentially contains no evidence at all.
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Consider, for instance, the argument that “Programs to provide greater access to health care are good because everyone should have access to medical care.” Nothing is substantively different between the statements that “Everyone should have access to medical care” and “Programs to provide greater access to health care are good.” Since the statements are generally the same, one cannot be taken as evidence for the other. If anyone believes one of the statements, they automatically believe the other. As Johnson and Blair (2006: 80) note, “If the conclusion is acceptable, then no argument is needed to support it”.
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21.2.1.2 The Fallacy of Incompatibility The fallacy of incompatibility also is a kind of problematic premise and, as such, is related to the standard of acceptability. Audiences rightfully expect a certain degree of consistency in evidence presented. Incompatibility occurs when evidence lacks, for any reason, that degree of consistency. When one piece of evidence is incompatible with another, the result is that the audience may consider neither piece of evidence as credible, and the claim will probably be unsuccessful.
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For example, when a debater offers a statement as evidence that is at odds with another statement offered by that debater at a different place or time, or when a debater’s argument is incompatible with some action that the debater performed or recommended elsewhere, the argument may be seen as including the fallacy of incompatibility.
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Consider, for instance, the case of a person who maintains that certain government programs are good, but in a different province, asserts that those programs have damaged the nation’s economy. Audiences are unlikely to find either statement acceptable as evidence because the statements are not incompatible with one another.
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Debaters who fail to meet the standard of acceptability may have committed a fallacy that is called a problematic premise. Begging the question and the fallacy of incompatibility are two specific kinds of problematic premises. Now, attention will shift from acceptability to fallacies related to the standards of relevance and sufficiency.
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21.2.2 Irrelevant Reasons
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This category of fallacies sometimes is called by its Latin name, non sequitor, meaning “It does not follow.” An irrelevant reason is one that, in combination with all other evidence offered, fails to minimally satisfy the criteria of relevance.