A fallacy is an argument which may convince some people but is not logically sound. Note that the truth of the conclusions of an argument does not determine whether the argument is a fallacy - it is the argument which is incorrect.
Fallacies can be categorized in a number of ways including:
Formal (or Logical) fallacies versus Informal fallacies
A formal fallacy relies on a logical step in a proof or argument which is incorrect allowing a conclusion to be reached. An informal fallacy will not occur in this manner.
Verbal fallacies
Which use some property of language, such as its ambiguity or length to mislead.
Though some of these classifications are not that sharp.
Fallacies are also often concerned with causality, which is not strictly addressed by logic, or involve implicit (or unstated) assumptions.
Fallacies often exploit emotional triggers in the listener or interlocutor, for example relating arguments to patriotism or family, or intellectual weaknesses targeting subjects which the listener knows little about. They may also take advantage of social relationships between people, for example citing support of important individuals to encourage listeners to agree with a conclusion..
When considered by themselves, fallacies can often seem very difficult to be misled by. However, actual 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.
Material fallacies
The taxonomy 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
Example Argument: Cutting people is a crime. Surgeons cut people. Therefore, surgeons are criminals.
Problem: Cutting people is only sometimes a crime. - 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
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. - 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; appeal to loyalty.),
fear (argumentum ad baculum),
conventional propriety (argumentum ad verecundiam--appeal to authority)
Example Argument: Kim Jong Il believes that war is justifiable therefore it must be justifiable.
Problem: Kim Jong Il can be wrong.
to arouse pity for getting one's conclusion accepted (argumentum ad misericordiam)
proving the proposition under dispute without any certain proof (argumentum ad ignoratiam) - 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 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. - Fallacy of False Cause or Non Sequitur (Latin for "it does not follow")--incorrectly assumes one thing is the cause of another
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).
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. - Fallacy of Many Questions (Plurium Interrogationum)--groups more than one question in the form of a single question
Example Argument: Is it true that you no longer consider yourself an anarchist?
Problem: A yes or no answer will still be an admission of guilt to being an anarchist at some point in time.
Example
The following argument is posited:
Cake is food.
Food is delicious.
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, 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
They are generally classified as follows.
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"
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
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.
Example Argument: "the university (the whole) is 700 years old, therefore, all the staff (each part) are 700 years old".
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.
Example 1
Tom argues:
Joe is a good tennis player.
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.
One posits the argument:
Nothing is better than eternal happiness.
Eating a hamburger is better than nothing.
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.
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.
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.
