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Fallacy Files

 

Ad Hominem
  • An ad hominem argument, also known as argumentum ad hominem (Latin: "argument to the person", "argument against the man") consists of replying to an argument by attacking or appealing to the person making the argument, rather than by addressing the substance of the argument.
  • You claim that this man is innocent, but you cannot be trusted since you are a criminal as well.
  • You feel that abortion should be legal, but I disagree, because you are uneducated and poor.
  • You can't believe Jack when he says there isn't any God because he doesn't even have a job.

Amphibology
  • Amphibology or amphiboly (from the Greek amphibolia) is, in logic, a verbal fallacy arising from ambiguity in the grammatical structure of a sentence.
  • Teenagers shouldn't be allowed to drive. It's getting too dangerous on the streets.
  • I once shot an elephant in my pajamas.
  • Dog for sale. Will eat anything. Especially fond of children.
  • At our drugstore, we dispense with accuracy!
  • (Professor to student, on receiving a fifty-page term paper): "I shall waste no time reading it."

Appeal to Authority
  • An appeal to authority or argument by authority is a type of argument in logic, consisting on basing the truth value of an otherwise unsupported assertion on the authority, knowledge or position of the person asserting it.
  • "My teacher said so, therefore it must be right."
  • Something must be true because a war hero says it.
  • Something must be true because it is in a sacred text.
  • Something must be true because there is a scientific consensus. 

Appeal to Consequences
  • Appeal to consequences is an argument that concludes a premise (typically a belief) to be either true or false based on whether the premise leads to desirable or undesirable consequences. This is based on an appeal to emotion and is considered to be a form of logical fallacy, since the appeal of a consequence does not address the truth value of the premise.
  • "Atheism must be erroneous: it denies eternal happiness after death."
  • "Religion is the opiate of humanity: if it were true, nobody would have free will."
  • "Enron cannot be guilty: think of all the shares our family owns."

Appeal to Emotion
  • Appeal to emotion is a logical fallacy which uses the manipulation of the listener's emotions, rather than valid logic, to win an argument. This kind of appeal to emotion is a type of red herring and encompasses several logical fallacies, including:
  • Appeal to consequences
  • Appeal to fear
  • Appeal to flattery
  • Appeal to pity
  • Appeal to ridicule
  • Appeal to spite
  • Wishful thinking

Appeal to Fear
  • An appeal to fear  is a logical fallacy in which a person attempts to create support for her or his idea by increasing fear and prejudice toward a competitor. The appeal to fear is extremely common in marketing and politics.
  • "Nobody ever got fired for buying IBM"
  • "If we don't introduce National ID cards, the terrorists have won."
  • "If the defendant is acquitted, there will be riots. Therefore, he is guilty."
  • "Believe in God or burn in Hell." (this also uses appeal to force)

Appeal to Flattery
  • Appeal to flattery is a logical fallacy in which a person uses flattery, excessive compliments, in an attempt to win support for their side.
  • "Surely a man as smart as you can see this is a brilliant proposal." (so, if you don't, it means you are stupid)
  • "I needed a beautiful woman to endorse my product, so naturally I thought of you." (so, if you don't accept, it means you're ugly)

Appeal to Pity
  • An appeal to pity  is a logical fallacy in which someone tries to win support for their argument or idea by exploiting their opponent's feelings of pity or guilt. The appeal to pity is a specific kind of appeal to emotion.
  • "I hope you like my proposal. It took me six years to write and I don't know what I'd do if you rejected it."
  • "I really deserve a raise. Unless I make more money I may lose my home."
  • "I hope you find the defendant not guilty of embezzlement. Just look at the poor guy, he's in a wheelchair. Show some sympathy!"

Begging the Question
  • In logic, begging the question, also known as circular reasoning and by the Latin name petitio principii, is an informal fallacy found in many attempts at logical arguments. An argument which begs the question is one in which a premise presupposes the conclusion in some way. Such an argument is valid in the sense in which logicians use that term, yet provides no reason at all to believe its conclusion.
  • "The Bible says God exists, and the Bible must be right since it is the revealed word of God, so God exists." Obviously enough, no one who doubts the conclusion has any reason to accept the second premise, which presupposes it. This is, of course, a blatant example meant solely to illustrate the fallacy; less contrived instances may be much more subtle.
  • A version of our first example that constitutes circular reasoning in this strict sense would involve asserting both:
  • The Bible tells me that faith in God is a good basis for forming beliefs
  • In general, what the Bible says is true
  • Therefore, faith in God is a good basis for belief
  • and
  • Faith in God is a good basis for forming beliefs
  • My faith in God tells me that, in general, what the Bible says is true
  • Therefore, in general, what the Bible says is true.

Biased Sample
  • A biased sample is one that is falsely taken to be typical of a population from which it is drawn. Someone saying "Everyone liked that movie!" might not mention that the "everyone" was them and three of their friends, or a group of the star's fans.
  • I wouldn't like to go to America because of all the gun crime, we see it on the news all the time.
  • Why do young people all take drugs and go around mugging old ladies? You read about it in the paper all the time!

Fallacy of the Accident
  • The logical fallacy of accident, also called destroying the exception, is a deductive fallacy occurring in statistical syllogisms (an argument based on a generalization) when an exception to the generalization is ignored.
  • Cars should never exceed the speed limit. Police cars are cars. Therefore, police cars should never exceed the speed limit.

  • Cutting people with a knife is a crime.
    Surgeons cut people with knives.
    Surgeons are criminals

 

Fallacy of the Single Cause
  • The fallacy of the single cause, also known as joint effect or causal oversimplification, is a logical fallacy of causation that occurs when it is assumed that there is one, simple cause of an outcome when in reality it may have been caused by a number of only jointly sufficient causes.
  • Often after a tragedy it is asked, "What was the cause of this?" Such language implies that there is one cause, when instead there were probably a large number of contributing factors. However, having produced a list of several contributing factors, it may be worthwhile to look for the strongest of the factors, or a single cause underlying several of them.
Generalization
  • Generalization is a foundational element of logic and human reasoning. It is the essential basis of all valid deductive inference.
  • The concept of generalization has broad application in many related disciplines, sometimes having a specialized context-specific meaning.

Hasty Generalization
  • Hasty generalization, also known as fallacy of insufficient statistics, fallacy of insufficient sample, fallacy of the lonely fact, leaping to a conclusion, hasty induction, law of small numbers, unrepresentative sample, is the logical fallacy of reaching an inductive generalization based on too little evidence. It commonly involves basing a broad conclusion upon the statistics of a survey of a small group that fails to sufficiently represent the whole population.
  • "I loved the hit song, therefore I'll love the album it's on". Fallacious because the album might have one good song and lots of filler.
  • "This Web site looks OK to me on my computer; therefore, it will look OK on your computer, too". Fallacious because different computers may present content differently.
  • "I got into a fight with a bunch of Asians today. They all knew 10 Animal Huo style Kung Fu. This means that all Asians know 10 Animal Huo style Kung Fu."
Irrelevant Conclusion
  • Irrelevant conclusion is the logical fallacy of presenting an argument that may in itself be valid, but which proves or supports a different proposition than the one it is purporting to prove or support.
  • A red herring is a deliberate attempt to change the subject or divert the argument from the real question at issue;
  • For instance, “Senator Jones should not be held accountable for cheating on his income tax. After all, there are other senators who have done far worse things.” Another example “I should not pay a fine for reckless driving. There are many other people on the street who are dangerous criminals and rapists, and the police should be chasing them, not harassing a decent tax-paying citizen like me.”
  • Baseball player Mark McGwire just retired. Clearly, he will end up in the Hall of Fame. After all, he's such a nice guy, and he gives a lot of money to all sorts of charities. (Friendliness and charity are not qualifications for induction into the Hall of Fame, therefore they do not support the conclusion.)
Logical Fallacies
  • In philosophy, a logical fallacy or a formal fallacy is a pattern of reasoning which is always or at least most commonly wrong. This is due to a flaw in the structure of the argument which renders the argument invalid. A formal fallacy is contrasted with an informal fallacy, which has a valid logical form, but is false due to one or more of its premises being false.
  • The term fallacy is often used more generally to mean an argument which is problematic for any reason, whether it be a formal or an informal fallacy.
  • The presence of a formal fallacy in a deductive argument does not imply anything about the argument's premises or its conclusion. 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.

Non Sequitur
  • A non sequitur is a conversational and literary device, often used for comical purposes (as opposed to its use in formal logic). It is a comment which, due to its lack of meaning relative to the comment it follows, is absurd to the point of being humorous or confusing. Its use can be deliberate or unintentional. Literally, it is Latin for "it does not follow."
  • A good example of this device can be seen in an episode of the Micallef Programme which features a game show segment called Non-Sequitur Family Feud. The presenter asks the question "Name ten things you plug in", to which the contestant answers correctly with a list of ten random phrases, including mules, Lewis Carroll, 1832 and "I like butterscotch".
  • The non sequitur can be understood as the converse of cliché. To illustrate: in theatre, traditional comedy and drama depend on the ritualization—that is, the predictability—of human emotional experiences. In contrast, the theatre of the absurd depends upon the disjunction—that is, the unpredictability—of that experience. Predictability in its most extreme form is cliché; unpredictability, then, expresses itself most naturally as non sequitur.
  • Blog on non sequitur
Overwhelming Exception
  • An overwhelming exception is a logical fallacy similar to a hasty generalization. It is a generalization which is accurate, but comes with one or more qualifications which eliminate so many cases that what remains is much less impressive than the initial statement might have led one to assume.
  • "Our foreign policy has always helped other countries, except of course when it is against our National Interest..." (The false implication is that our foreign policy always helps other countries).
  • "All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us?" (The attempted implication (fallaciously false in this case) is that the Romans did nothing for us). This is a quotation from Monty Python's Life of Brian.

Proof by Verbosity
  • Proof by verbosity is a term used to describe an excessively verbose mathematical proof that may or may not actually prove the result. Such proofs are most often presented by students who don't fully grasp the concepts they are writing about. Students presenting such proofs often either hope to hide their lack of understanding or are uncertain how extensive their proof is expected to be.
  • Proof by verbosity should not be confused with proof by exhaustion, the latter being a valid form of proof. The difference lies in that a proof by exhaustion is used when a number of dissimilar cases must be independently proven, whereas a proof by verbosity tends to be repetitive, with many overlapping proofs for specific cases of a more general problem.

Slippery Slope
  • It suggests that an action will initiate a chain of events culminating in an undesirable event later. The argument is sometimes referred to as the thin end of the wedge or the camel's nose. The slippery slope can be valid or fallacious.
  • An effective procedure for checking whether a propositional formula is a tautology or not is by means of truth tables.
  • Slippery slope can also be used as a retort to the establishment of arbitrary boundaries or limitations. For example, one might argue that rent prices must be kept to $1,000 or less a month to be affordable to tenants in an area of a city. A retort invoking the slippery slope could go in two different directions:
  • Once such price ceilings become accepted, they could be slowly lowered, eventually driving out the landlords and worsening the problem.
  • If a $1,000 monthly rent is affordable, why isn't $1,025 or $1,050? By lumping the tenants into one abstract entity, the argument renders itself vulnerable to a slippery slope argument. A more careful argument in favor of price ceilings would statistically characterize the number of tenants who can afford housing at various levels based on income and choose a ceiling that achieves a specific goal, such as housing 80% of the working families in the area.
Tautology
  • In logic, a tautology is a statement containing more than one sub-statement, that is true regardless of the truth values of its parts. For example, the statement "Either all crows are black, or not all of them are", is a tautology, because it is true no matter what color crows are.
  • An effective procedure for checking whether a propositional formula is a tautology or not is by means of truth tables.
  • As an efficient procedure, however, truth tables are constrained by the fact that the number of logical interpretations (or truth-value assignments) that have to be checked increases as 2k, where k is the number of variables in the formula. Algebraic, symbolic, or transformational methods of simplifying formulas quickly become a practical necessity to overcome the "brute-force", exhaustive search strategies of tabular decision procedures.
Undistributed Middle
  • The fallacy of the undistributed middle is a logical fallacy that is committed when the middle term in a categorical syllogism isn't distributed. It is thus a syllogistic fallacy.
  • All students carry backpacks.
    My grandfather carries a backpack.
    Therefore, my grandfather is a student.

Validity
  • In logic, the form of an argument is valid precisely if it cannot lead from true premises to a false conclusion. An argument is said to be valid if, in every model in which all premises are true, the conclusion is true. For example: "All A are B; some A are C; therefore some B are C" is a valid form.
  • A formula of logic is said to be valid if it is true under every interpretation (also called structure or model).

Wishful Thinking
  • Wishful thinking is the formation of beliefs and making decisions according to what might be pleasing to imagine instead of by appealing to evidence or rationality.
  • Studies have consistently shown that, holding all else equal, subjects will predict positive outcomes to be more likely than negative outcomes.
  • Economist Irving Fisher said that "stock prices have reached what looks like a permanently high plateau" a few weeks before Stock Market Crash of 1929, which was followed by the Great Depression.
  • President John F. Kennedy believed that, if overpowered by Cuban forces, the CIA-backed rebels could "escape destruction by melting into the countryside" in the Bay of Pigs fiasco.