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A fallacy is an argument which seems convincing but is not logically sound. The truth of the conclusions of an argument does not determine whether the argument is a fallacy - it is the argument which is fallacious.

Fallacies can be categorized in a number of ways, including:

Formal (or Logical) fallacies versus Informal fallacies
A formal fallacy relies on an incorrect logical step. An informal fallacy does not rely on incorrect logical deduction.
Verbal fallacies
Verbal fallacies use some property of language to mislead. For example, ambiguity or verbosity.

A fallacy may fall into one classification.

Fallacies are also often concerned with causality, which is not strictly addressed by logic. They may also involve implicit (or unstated) assumptions.

Fallacies often exploit emotional triggers in the listener or interlocutor. For example, an argument may appeal to patriotism or family or may exploit an intellectual weakness of the listener. Fallacious arguments may also take advantage of social relationships between people. For example, citing support of important individuals to encourage listeners to agree with a conclusion.

Considered by themselves, fallacies can often seem obvious. However, arguments are often structured using rhetorical patterns that obscure the logical argument - deliberately or not - making observing fallacies difficult. Also, the component parts of the fallacy may be spread over a large period of time.


[edit] Material fallacies

The taxonomy of material fallacies is widely adopted by modern logicians and is based on that of Aristotle, Organon (Sophistici elenchi). This taxonomy is as follows:

  • Fallacy of Accident: a generalization that disregards exceptions
    • Example
      Argument: Cutting people is a crime. Surgeons cut people. Therefore, surgeons are criminals.
      Problem: Cutting people is only sometimes a crime.
    • Also called destroying the exception, a dicto simpliciter ad dictum secundum quid
  • Converse Fallacy of Accident: argues from a special case to a general rule
    • Example
      Argument: Every swan I have seen is white, so it must be true that all swans are white.
      Problem: What one has seen is a special case. One can not have seen all swans.
    • Also called reverse accident, destroying the exception, a dicto secundum quid ad dictum simpliciter
  • 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
    • Example:
      Example Argument: If a person runs barefoot, then his feet hurt. Socrates' feet hurt. Therefore, Socrates ran barefoot.
      Problem: 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
    • Example
      Argument: 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.
      Problem: Other illnesses may cause sore throat.
  • Begging the question: demonstrates a conclusion by means of premises that assume that conclusion.
    • Example
      Argument: Paul must be telling the truth, because I have heard him say the same thing many times before.
      Problem: Paul may be consistent in what he says, but he may have been lying the whole time.
    • Also called Petitio Principii, Circulus in Probando, arguing in a circle, assuming the answer
  • Fallacy of False Cause or Non Sequitur:: incorrectly assumes one thing is the cause of another. Non Sequitur is Latin for "It does not follow."
    • Example
      Argument: Our nation will prevail because God is great.
      Problem: One has no reason to believe that simply because God is great he will cause a nation to prevail.
    • Special cases
      • post hoc ergo propter hoc: believing that temporal succession implies a causal relation.
      • cum hoc ergo propter hoc: believing that happenstance implies causal relation (aka as fallacy of causation versus correlation: assumes that correlation implies causation).
  • Fallacy of Many Questions: groups more than one question in the form of a single question
    • Example
      Argument: Is it true that you no longer beat your wife?
      Problem: A yes or no answer will still be an admission of guilt to beating your wife at some point in time.
    • Also called Plurium Interrogationum

[edit] Example

Consider the following argument which claims to prove that pie is delicious:

  1. Pie is food.
  2. Food is delicious.
  3. Therefore, pie is delicious.

This particular argument has the form of a categorical syllogism. In this case "Pie is food." and "Food is delicious." act as premises. The first assumption is almost true by definition: pie is a foodstuff edible by humans. The second assumption is less clear; 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.

Only the first interpretation validates the second premise. If the interlocutor grants this interpretation then the argument is valid; the interlocutor is essentially conceding the point. However, the interlocutor is more likely to believe that some food is not delicious. In this case, the speaker must prove the assertion that pie is a unique type of universally delicious food. This is a disguised form of the original thesis. In this case, the speaker commits the logical fallacy of begging the question.

[edit] 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
Example Argument: All heavy things have a great mass; this is heavy fog; therefore this fog has a great mass.
Problem: Heavy describes more than just weight. In the case of fog it means that the fog is dense not that it has a great mass"
  • Amphibology is the result of ambiguity of grammatical structure
Example: The position of the adverb "only" in the a sentence starting with "He only said that" results in a sentence in which it is uncertain as to which of the other three words the speaker is intending to modify with the adverb.
  • Fallacy of Composition "From Each to All". Arguing from some property of constituent parts, to the conclusion that the composite item has that property. This can be acceptable (i.e., not a fallacy) 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")
Example Argument: All the band members (constituent parts) are highly skilled, therefore the band (composite item) is highly skilled.
Problem: The band members may be skilled musicians but not in the same styles of music.
  • Division, the converse of the preceding, arguing from a property of the whole, to each constituent part
Example Argument: "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.[citation needed]
  • Figure of Speech, the confusion between the metaphorical and ordinary uses of a word or phrase.
Example: The sailor was at home on the sea.
Problem: The expression 'to be at home' does not literally mean that ones home is in that location.
  • Fallacy of Misplaced Concretion, identified by Whitehead in his discussion of metaphysics, this refers to the reification of concepts which exist only in discourse.

[edit] 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.

[edit] 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 equivocation.

[edit] 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.

[edit] Formalisms and frameworks used to understand fallacies

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.

[edit] 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.

[edit] Fallacies in the media and politics

"Either you're for me, or against me" is a common logical fallacy (a 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[citation needed] . 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.

[edit] History of the study of fallacies

Fallacies were studied by the Ancient Greeks. Aristotle discussed fallacies in De Sophistici Elenchi.

[edit] Origins of names

Many logical fallacies are named by Latin phrases. Ad Hominem, argumentum ad populum, and post hoc ergo propter hoc are just a few examples.

[edit] See also

[edit] References

[edit] External links

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