fallacy

fallacy, in logic, a term used to characterize an invalid argument. Strictly speaking, it refers only to the transition from a set of premises to a conclusion, and is distinguished from falsity, a value attributed to a single statement. The laws of syllogisms were systematically elaborated by Aristotle, and for an argument to be valid, it must adhere to all the laws; to be fallacious, it need only break one (see syllogism). The term fallacy has come to be used in a somewhat wider sense than the purely formal one. Informal fallacies are said to occur when statements are ambiguous or vague as to the logical form they represent, or when a multiplicity of meaning is present and the validity of the argument depends on switching meanings of a word or a phrase in midstream.

In philosophy, reasoning that fails to establish its conclusion because of deficiencies in form or wording. Formal fallacies are types of deductive argument that instantiate an invalid inference pattern (see deduction; validity); an example is “affirming the consequent: If A then B; B; therefore, A.” Informal fallacies are types of inductive argument the premises of which fail to establish the conclusion because of their content. There are many kinds of informal fallacy; examples include argumentum ad hominem (“argument against the man”), which consists of attacking the arguer instead of his argument; the fallacy of false cause, which consists of arguing from the premise that one event precedes another to the conclusion that the first event is the cause of the second; the fallacy of composition, which consists of arguing from the premise that a part of a thing has a certain property to the conclusion that the thing itself has that property; and the fallacy of equivocation, which consists of arguing from a premise in which a term is used in one sense to a conclusion in which the term is used in another sense.

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A fallacy is a component of an argument which, being demonstrably flawed in its logic or form, renders the argument invalid in whole.

Types of fallacies

In logical arguments, fallacies are either formal or informal. Because the validity of a deductive argument depends on its form, a formal 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 (or equivocations).

Recognizing fallacies in actual arguments may be difficult since arguments are often structured using rhetorical patterns that obscure the logical connections between assertions. Fallacies may also exploit the emotional or intellectual weaknesses of the interlocutor. Having the capability of recognizing logical fallacies in arguments reduces the likelihood of such an occurrence.

A different approach to understanding and classifying fallacies is provided by argumentation theory; see for instance the van Eemeren, Grootendorst reference below. In this approach, an argument is regarded as an interactive protocol between individuals which attempts to resolve a disagreement. The protocol is regulated by certain rules of interaction, and violations of these rules are fallacies. Many of the fallacies in the list below are best understood as being fallacies in this sense.

Fallacious arguments involve not only formal logic but also causality. Others may involve psychological ploys such as use of power relationships between proposer and interlocutor to establish necessary intermediate (explicit or implicit) premises for an argument. Fallacies often have unstated assumptions or implied premises in arguments that are not always obvious at first glance.

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 as to why the conclusion is true is not valid. See argument from fallacy.

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)--makes a generalization that disregards exceptions (e.g., Cutting people is a crime. Surgeons cut people. Therefore, surgeons are criminals.)
• Converse Fallacy of Accident (also called reverse accident, destroying the exception, or a dicto secundum quid ad dictum simpliciter)--argues from a special case to a general rule (e.g., Every swan I have seen is white, so it must be true that all swans are white..)
• Irrelevant Conclusion (also called Ignoratio Elenchi)--diverts attention away from a fact in dispute rather than address it directly. This is sometimes referred to as a "red herring". Subsets include:
• purely personal considerations (argumentum ad hominem),
• popular sentiment (argumentum ad populum--appeal to the majority),
• fear (argumentum ad baculum),
• conventional propriety (argumentum ad verecundiam--appeal to authority)

• Affirming the Consequent--draws a conclusion from premises that do not support that conclusion by assuming Q implies P on the basis that P implies Q (e.g., If a person runs barefoot, then his feet hurt. Socrates' feet hurt. Therefore, Socrates ran barefoot. Other things, such as tight sandals, can result in sore feet.)
• Denying the antecedent--draws a conclusion from premises that do not support that conclusion by assuming Not P implies Not Q on the basis that P implies Q (e.g., If I have the flu, then I have a sore throat. I do not have the flu. Therefore, I do not have a sore throat. Other illnesses may cause sore throat.)
• Begging the question (also called Petitio Principii, Circulus in Probando--arguing in a circle, or assuming the answer)--demonstrates a conclusion by means of premises that assume that conclusion (e.g., Paul must be telling the truth, because I have heard him say the same thing many times before. Paul may be consistent in what he says, but he may have been lying the whole time.)
• Call to Perfection is committed when one argues to postpone some action or policy until some unlikely event or impossible change is achieved. (example: I'll do it the day that pigs can fly. Since pigs do not fly and will probably never be able to, the action or policy will probably never take place.)
• Fallacy of False Cause or Non Sequitur (Latin for "it does not follow")--incorrectly assumes one thing is the cause of another (e.g., Our nation will prevail because God is great.)
• A special case of this fallacy also goes by the Latin term post hoc ergo propter hoc--the fallacy of believing that temporal succession implies a causal relation.
• Another special case is given by the Latin term cum hoc ergo propter hoc -- the fallacy of believing that happenstance implies causal relation (aka as fallacy of causation versus correlation: assumes that correlation implies causation).

• Fallacy of Many Questions (Plurium Interrogationum)--groups more than one question in the form of a single question (e.g., Is it true that you no longer beat your wife? A yes or no answer will still be an admission of guilt to wife-beating.)

Example

The following argument is posited:

1. Cake is food.
2. Food is delicious.
3. Therefore, cake is delicious.

This argument claims to prove that cake 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: cake 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:

• All food is delicious.
• One particular type of food is delicious.
• Most food is delicious.
• To me, all food is delicious.
• Some food is delicious.

In all but the first interpretation, the above syllogism would then fail to have validated its second premise. The person 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 that person. However, the interlocutor is more likely to believe that some food is disgusting, such as a frog's liver white chocolate torte with mustard; and in this case the person is not much better off than he was before he formulated the argument, since he now has to prove the assertion that cake 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, the person commits the logical fallacy of begging the question.

Verbal fallacies

Verbal fallacies are those in which a 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 heavy things have a great mass; This is heavy fog; therefore this fog has a great mass").
• Connotation fallacies occur when a dysphemistic word is substituted for the speaker's actual quote and used to discredit the argument. It is a form of attribution fallacy.
• Amphibology is the result of ambiguity of grammatical structure, e.g. of the position of the adverb "only" in careless writers ("He only said that," in which sentence, the adverb has been intended to qualify any one of the other three words).
• Fallacy of Composition "From Each to All". Arguing from some property of constituent parts, to the conclusion that the composite item has that property e.g. "all the band members (constituent parts) are highly skilled, therefore the band (composite item) is highly skilled". This can be acceptable with certain arguments such as spatial arguments e.g. "all the parts of the car are in the garage, therefore the car is in the garage"
• Division, the converse of the preceding, arguing from a property of the whole, to each constituent part e.g. "the university (the whole) is 700 years old, therefore, all the staff (each part) are 700 years old".
• Proof by verbosity, sometimes colloquially referred to as argumentum verbosium - a rhetorical technique that tries to persuade by overwhelming those considering an argument with such a volume of material that the argument sounds plausible, superficially appears to be well-researched, and it is so laborious to untangle and check supporting facts that the argument might be allowed to slide by unchallenged.
• 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 deprecation of a popular hero, or it may imply that the person in question is a deplorable pianist.
• Figure of Speech, the confusion between the metaphorical and ordinary uses of a word or phrase.
• Fallacy of Misplaced Concretion, identified by Whitehead in his discussion of metaphysics, this refers to the reification of concepts which exist only in discourse.

Example 1

Tom argues:

1. Joe is a good tennis player.
2. Therefore, Joe 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, Tom says that Joe is good at some particular activity, in this case tennis. In the conclusion, Tom states that Joe 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: Joe 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 Tom. Nothing concerning Joe'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 2

One posits the argument:

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.

These sort of fallacies are firmly tied to English language and how the words are used in ambiguous ways in several expressions. The phrase "nothing is better than X" actually means "Such a thing that would be better than X does not exist". If the arguments mentioned in this article were to be translated to other languages, they would suddenly make no sense at all since the word "nothing" would be translated differently in different sentences.

Deductive fallacy

In philosophy, the term logical fallacy properly refers to a formal fallacy : a flaw in the structure of a deductive argument which renders the argument invalid.

However, it is often used more generally in informal discourse to mean an argument which is problematic for any reason, and thus encompasses informal fallacies as well as formal fallacies. – valid but unsound claims or bad nondeductive argumentation – .

The presence of a formal fallacy in a deductive argument does not imply anything about the argument's premises or its conclusion (see fallacy fallacy). Both may actually be true, or even more probable as a result of the argument (e.g. appeal to authority), but the deductive argument is still invalid because the conclusion does not follow from the premises in the manner described. By extension, an argument can contain a formal fallacy even if the argument is not a deductive one; for instance an inductive argument that incorrectly applies principles of probability or causality can be said to commit a formal fallacy.

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. DEDUCTIVE REASONING: drawing a conclusion from facts/data.

Fallacies in the media and politics

"Either you're for me, or against me" unknown but common fallacy (False dilemma).

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.

See also

• List of fallacies
• Attacking Faulty Reasoning
• Truth
• Evidence
• List of cognitive biases

References

• Aristotle, On Sophistical Refutations, De Sophistici Elenchi.
• William of Ockham, Summa of Logic (ca. 1323) Part III.4.
• John Buridan, Summulae de dialectica Book VII.
• Francis Bacon, the doctrine of the idols in Novum Organum Scientiarum, Aphorisms concerning The Interpretation of Nature and the Kingdom of Man, XXIIIff
• The Art of Controversy | Die Kunst, Recht zu behalten - The Art Of Controversy (bilingual), by Arthur Schopenhauer (also known as "Schopenhauers 38 stratagems")
• John Stuart Mill, A System of Logic - Raciocinative and Inductive Book 5, Chapter 7, Fallacies of Confusion
• C. L. Hamblin, Fallacies Methuen London, 1970.
• Fearnside, W. Ward and William B. Holther, Fallacy: The Counterfeit of Argument, 1959.
• Vincent F. Hendricks, Thought 2 Talk: A Crash Course in Reflection and Expression, New York: Automatic Press / VIP, 2005, ISBN 87-991013-7-8
• D. H. Fischer, Historians' Fallacies: Toward a Logic of Historical Thought, Harper Torchbooks, 1970.
• Douglas N. Walton, Informal logic: A handbook for critical argumentation. Cambridge University Press, 1989.
• F. H. van Eemeren and R. Grootendorst, Argumentation, Communication and Fallacies: A Pragma-Dialectical Perspective, Lawrence Erlbaum and Associates, 1992.
• Warburton Nigel, Thinking from A to Z, Routledge 1998.
• T. Edward Damer. Attacking Faulty Reasoning, 5th Edition, Wadsworth, 2005. ISBN 0-534-60516-8
• Sagan, Carl, "The Demon-Haunted World: Science As a Candle in the Dark". Ballantine Books, March 1997 ISBN 0-345-40946-9, 480 pgs. 1996 hardback edition: Random House, ISBN 0-394-53512-X, xv+457 pages plus addenda insert (some printings). Ch.12.

External links

• Fallacy files contains categorization of fallacies with examples.
• 42 informal logical fallacies explained by Dr. Michael C. Labossiere (including examples)
• List of fallacies with clear examples
• Logical Fallacies and the Art of Debate
• Logical Fallacies.Info
• An Informal Fallacy Primer
• Stephen Downes Guide to the Logical Fallacies