From Academic Kids

The term fallacy denotes any mistaken statement used in an argument. In logic, it specifically means an argument that violates the rules of formal demonstration. Beginning with Aristotle, fallacies have generally been placed in one of three categories: a material fallacy (misstatement of facts), a verbal fallacy (improper use of words), or a logical fallacy (also called a formal fallacy—a mistake in the process of inference). The latter two fallacies are called fallacies in dictione (L., in delivery) or in voce (L., in expression), as opposed to material fallacies in re (L. in fact/cause/property) or extra dictionem (outside of/beside delivery).


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:

  • Fallacy of Accident (also called destroying the exception or a dicto simpliciter ad dictum secundum quid) meaning to argue erroneously from a general rule to a particular case, without proper regard to particular conditions which vitiate the application of the general rule; e.g. if manhood suffrage be the law, arguing that a criminal or a lunatic must, therefore, have a vote
  • Converse Fallacy of Accident (also called reverse accident, destroying the exception, or a dicto secundum quid ad dictum simpliciter) meaning to argue from a special case to a general rule
  • Irrelevant Conclusion (also called Ignoratio Elenchi), wherein, instead of proving the fact in dispute, the arguer seeks to gain his point by diverting attention to some extraneous fact (as in the legal story of " No case. Abuse the plaintiff's attorney "). The fallacies are common in platform oratory, in which the speaker obscures the real issue by appealing to his audience on the grounds of
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.
  • Begging the question (also called Petitio Principii or Circulus in probando--arguing in a circle) consists in demonstrating a conclusion by means of premises which pre-suppose that conclusion. Jeremy Bentham points out that this fallacy may lurk in a single word, especially in an epithet, e.g. if a measure were condemned simply on the ground that it is alleged to be " un-English "
  • Fallacy of the Consequent, really a species of Irrelevant Conclusion, wherein a conclusion, is drawn from premises which do not really support it
  • Fallacy of False Cause, or Non Sequitur (L., it does not follow), wherein one thing is in-correctly assumed as the cause of another, as when the ancients attributed a public calamity to a meteorological phenomenon;
  • Fallacy of Many Questions (Plurium Interrogationum), wherein several questions are improperly grouped in the form of one, and a direct categorical answer is demanded, e.g. if a prosecuting counsel asked the prisoner " What time was it when you met this man? " with the intention of eliciting the tacit admission that such a meeting had taken place.

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.

  • Equivocation consists in employing the same word in two or more senses, e.g. in a syllogism, the middle term being used in one sense in the major and another in the minor premise, so that in fact there are four not three terms (" All fair things are honourable; This woman is fair; therefore this woman is honourable," the second " fair " being in reference to complexion)..,
  • Amphibology is the result of ambiguity of grammatical structure, e.g. of the position of the adverb " only " in careless writers (" Be only said that," in which sentence, as experience shows, the adverb has been intended to qualify any one of the other three words).
  • Fallacy of Composition is a species of Amphibology, which results from the confused use of collective terms. e.g. "The angles of a triangle are less than two right angles" might refer to the angles separately or added together.
  • Division, the converse, of the preceding, which consists in employing the middle term distributively in the minor and collectively in the major premise.
  • Accent, which occurs only in speaking and consists of emphasizing the wrong word in a sentence. E.g., "He is a fairly good pianist," according to the emphasis on the words, may imply praise of a beginner's progress, or an expert's depreciation of a popular hero, or it may imply that the person in question is a deplorable violinist).
  • Figure of Speech, the confusion between the metaphorical and ordinary uses of a word or phrase.

Aristotelian logical fallacies

The standard 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.

Examples of fallacious arguments

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. Application of the death penalty is killing a human being.
  2. Killing a human being is wrong.
  3. Therefore, application of the death penalty is wrong.

This argument claims to prove the death penalty is wrong. 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: the death penalty is the judicially ordered execution of a prisoner as a punishment for a serious crime. 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:

  • Every act of killing a human being is wrong.
  • Most acts of killing a human being are wrong.
  • All acts of killing a human being are wrong, except those that are carried out for some legitimate purpose such as deterring serious crime.
  • Some acts of killing a human being are wrong.

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 every act of killing is wrong; 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 some acts of killing are not wrong, for instance those carried out in self defense or in legitimate warfare; 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 the death penalty is not a legimate form of killing, which is a disguised form of the original thesis. From the point of view 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. 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

A humorous variant of the fallacy of ambiguity is as follows. 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 which 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 acts of killing human beings are legal in this state.
  2. Some acts of killing human beings are illegal in this state.
  3. Therefore some acts of killing human beings are both legal and illegal in this state.

This is fallacious. Indeed, there is no logical principle which states

  1. For some x, P(x).
  2. For some y, Q(y).
  3. Then for some z, P(z) and Q(z).

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.

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, that is the premise which makes the argument unsound.

See also

Logical fallacy


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