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Fallacy

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A fallacy is a component of an argument that is demonstrably flawed in its logic or form, thus rendering the argument invalid (except in the case of begging the question) in whole. In logical arguments, fallacies are either formal or informal. Because the validity of a deductive argument depends on its form, a formal fallacy (or logical fallacy) is a deductive argument that has an invalid form, whereas an informal fallacy is any other invalid mode of reasoning whose flaw is not in the form of the argument.

Beginning with Aristotle, informal fallacies have generally been placed in one of several categories, depending on the source of the fallacy. There are fallacies of relevance, fallacies involving causal reasoning, and fallacies resulting from ambiguities. A similar approach to understanding and classifying fallacies is provided by argumentation theory. In this approach, an argument is regarded as part of an interactive protocol between individuals who are attempting to resolve a disagreement. The protocol is regulated by certain rules of interaction and violations of these rules are fallacies.

Recognizing fallacies in actual arguments may be difficult since arguments are often structured using rhetorical patterns that obscure the logical connections between assertions. As we illustrate with various examples, fallacies may also exploit the emotions or intellectual or psychological weaknesses of the interlocutor. Having the capability of recognizing logical fallacies in arguments will hopefully reduce the likelihood of such an occurrence.

Contents

Aristotelian fallacies

Material fallacies

The classification of material fallacies widely adopted by modern logicians and based on that of Aristotle, Organon (Sophistici elenchi), is as follows:
This fallacy has been illustrated by ethical or theological arguments wherein the fear of punishment is subtly substituted for abstract right as the sanction of moral obligation.

Verbal fallacies

Verbal fallacies are those in which a false conclusion is obtained by improper or ambiguous use of words. They are generally classified as follows.

Logical fallacies

The standard Aristotelian logical fallacies are:

Other systems of classification

Of other classifications of fallacies in general the most famous are those of Francis Bacon and J. S. Mill. Bacon (Novum Organum, Aph. 33, 38 sqq.) divided fallacies into four Idola (Idols, i.e. False Appearances), which summarize the various kinds of mistakes to which the human intellect is prone. With these should be compared the Offendicula of Roger Bacon, contained in the Opus maius, pt. i. J. S. Mill discussed the subject in book v. of his Logic, and Jeremy Bentham's Book of Fallacies (1824) contains valuable remarks. See Rd. Whateley's Logic, bk. v.; A. de Morgan, Formal Logic (1847) ; A. Sidgwick, Fallacies (1883) and other textbooks.

Fallacies in the media and politics

Fallacies are used frequently by pundits in the media and politics. When one politician says to another, "You don't have the moral authority to say X", this could be an example of the argumentum ad hominem or personal attack fallacy; that is, attempting to disprove X, not by addressing validity of X but by attacking the person who asserted X. Arguably, the politician is not even attempting to make an argument against X, but is instead offering a moral rebuke against the interlocutor. For instance, if X is the assertion:

The military uniform is a symbol of national strength and honor.
Then ostensibly, the politician is not trying to prove the contrary assertion. If this is the case, then there is no logically fallacious argument, but merely a personal opinion about moral worth. Thus identifying logical fallacies may be difficult and dependent upon context.

In the opposite direction is the fallacy of argument from authority. A classic example is the ipse dixit—"He himself said it" argument—used throughout the Middle Ages in reference to Aristotle. A modern instance is "celebrity spokespersons" in advertisements: a product is good and you should buy/use/support it because your favorite celebrity endorses it.

An appeal to authority is always a logical fallacy, though it can be an appropriate form of rational argument if, for example, it is an appeal to expert testimony. In this case, the expert witness must be recognized as such and all parties must agree that the testimony is appropriate to the circumstances. This form of argument is common in legal situations.

By definition, arguments with logical fallacies are invalid, but they can often be (re)written in such a way that they fit a valid argument form. The challenge to the interlocutor is, of course, to discover the false premise, i.e. the premise that makes the argument unsound.

General list of fallacies

The entries in the following list are neither exhaustive nor mutually exclusive; that is, several distinct entries may refer to the same pattern. As noted in the introduction, these fallacies describe erroneous or at least suspect patterns of argument in general, not necessarily argument based on formal logic. Many of the fallacies listed are traditionally recognized and discussed in works on critical thinking; others are more specialized.

General examples

Fallacious arguments involve not only formal logic but also causality. Others involve psychological ploys such as use of power relationships between proposer and interlocutor, appeals to patriotism and morality, appeals to ego etc., to establish necessary intermediate (explicit or implicit) premises for an argument. Indeed, fallacies very often lay in unstated assumptions or implied premises in arguments that are not always obvious at first glance. One way to obscure a premise is through enthymeme.

We now give a few examples illustrating common errors in reasoning. Note that providing a critique of an argument has no relation to the truth of the conclusion. The conclusion could very well be true, while the argument itself is not valid. See argument from fallacy.

In the following, we view an argument as a dialogue between a proposer and an interlocutor.

Example 1: Material Fallacy

James argues:

  1. Cheese is food.
  2. Food is delicious.
  3. Therefore, cheese is delicious.
This argument claims to prove that cheese is delicious. This particular argument has the form of a categorical syllogism. Any argument must have premises as well as a conclusion. In this case we need to ask what the premises are, that is the set of assumptions the proposer of the argument can expect the interlocutor to grant. The first assumption is almost true by definition: cheese is a foodstuff edible by humans. The second assumption is less clear as to its meaning. Since the assertion has no quantifiers of any kind, it could mean any one of the following:

In any of the last three interpretations, the above syllogism would then fail to have validated its second premise. James may try to assume that his interlocutor believes that all food is delicious; if the interlocutor grants this then the argument is valid. In this case, the interlocutor is essentially conceding the point to James. However, the interlocutor is more likely to believe that some food is disgusting, such as a sheep's liver white chocolate torte; and in this case James is not much better off than he was before he formulated the argument, since he now has to prove the assertion that cheese is a unique type of universally delicious food, which is a disguised form of the original thesis. From the point of view of the interlocutor, James commits the logical fallacy of begging the question.

Example 2: Verbal Fallacy

Barbara argues:

  1. Andre is a good tennis player.
  2. Therefore, Andre is 'good', that is to say a morally good person.
Here the problem is that the word good has different meanings, which is to say that it is an ambiguous word. In the premise, Barbara says that Andre is good at some particular activity, in this case tennis. In the conclusion, she says that Andre is a morally good person. These are clearly two different senses of the word "good". The premise might be true but the conclusion can still be false: Andre might be the best tennis player in the world but a rotten person morally. However, it is not legitimate to infer he is a bad person on the ground there has been a fallacious argument on the part of Barbara. Nothing concerning Andre's moral qualities is to be inferred from the premise. Appropriately, since it plays on an ambiguity, this sort of fallacy is called the fallacy of equivocation, that is, equating two incompatible terms or claims.

Example 3: Verbal Fallacy

Ramesh argues:

  1. Nothing is better than eternal happiness.
  2. Eating a hamburger is better than nothing.
  3. Therefore, eating a hamburger is better than eternal happiness.
This argument has the appearance of an inference that applies transitivity of the two-placed relation is better than, which in this critique we grant is a valid property. The argument is an example of syntactic ambiguity. In fact, the first premise semantically does not predicate an attribute of the subject, as would for instance the assertion

A potato is better than eternal happiness.
In fact it is semantically equivalent to the following universal quantification:

Everything fails to be better than eternal happiness.
So instantiating this fact with eating a hamburger, it logically follows that

Eating a hamburger fails to be better than eternal happiness.
Note that the premise A hamburger is better than nothing does not provide anything to this argument. This fact really means something such as

Eating a hamburger is better than eating nothing at all.
Thus this is a fallacy of composition.

Example 4: Logical Fallacy

In the strictest sense, a logical fallacy is the incorrect application of a valid logical principle or an application of a nonexistent principle:

  1. Some drivers are men.
  2. Some drivers are women.
  3. Therefore, some drivers are both men and women.
This is fallacious. Indeed, there is no logical principle that states

  1. For some x, P(x).
  2. For some x, Q(x).
  3. Therefore for some x, P(x) and Q(x).
An easy way to show the above inference is invalid is by using Venn diagrams. In logical parlance, the inference is invalid, since under at least one interpretation of the predicates it is not validity preserving.

See also

 

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