Difference between revisions of "Logical fallacy"

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A '''Logical fallacy''' is any argument that suffers from a crippling logical flaw.
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A '''logical fallacy''' is an error in [[formal logic|logical]] reasoning. While the common usage of the word ''fallacy'' would include ''any'' error in [[reason]]ing, in logic a fallacy is defined at a particularly [[deceit|deceptive]] argument which seems correct, but upon further examination is found to be incorrect.<ref name="copi">Copi, Irving M. and Carl Cohen. "Introduction to Logic, 12e". Pearson Education: 2005</ref>
  
[[Logic]] is a demanding discipline. Conclusions either follow from certain previously stated premises, or they do not. This is not, however, to say that a conclusion is always false if the argument supporting it is invalid. For example:
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Logical fallacies fall into two general categories: formal fallacies and informal fallacies. Formal fallacies apply to [[deductive argument]]s, and are those which relate to an improper application of a rule, whereas informal fallacies apply to [[inductive argument]]s, and are those which involve the improper use of the content of an argument.
  
#All undergraduates are human.
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A logical fallacy ''is not'' the same as [[lie|lying]]. A ''lie'' in logic is a [[premise]] that one offers while knowing that it is false.  
#All sophomores are human.
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#Therefore, all sophomores are undergraduates.
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One could as easily argue that all undergraduates are also sophomores, and the argument would be equally valid--or invalid in this case. However, one can establish the truth of the conclusion in another way--in this case, by [[definition]].
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There are four general categories of fallacies: fallacies of relevance, fallacies of defective or weak induction, fallacies of presumption, and fallacies of ambiguity.
  
Logical fallacy ''is not'' the same as lying. A ''lie'' in logic is a premise that one offers while knowing that it is false. False premises can still be part of valid arguments, but conclusions having false premises to support them will be unreliable. A logical fallacy, then, is a flawed argumental structure, one that would lead to an unreliable conclusion even when its premises are true.
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==Fallacies of Relevance==
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Fallacies of relevance are fallacies which are due to a lack of a relevant logical connection between [[premise]] and [[conclusion]].
  
The following is a catalog of logical fallacies, with each one given a separate heading, to make them easier to cite in other articles.
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===Appeal to force===
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An appeal to [[force]] (Lat: ''argumentum ad baculum'') is an argument which uses a threat of [[violence]] or force as a justification for the conclusion. An appeal to force argument follows the form:
  
==Catalog of Logical Fallacies==
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*If person A does not accept P, then Q
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*Q is a threat of force
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*Therefore P is true
  
===Argumentum ad hominem===
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For example: "If you do not pay me $30 I will break your leg. Therefore you owe me $30."
  
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===Appeal to pity===
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Also called [[emotion]]al appeal, (Lat: ''ad misericordiam'') this fallacy is characterized by a use of emotion as a justification for the conclusion. An appeal to [[pity]] follows the form:
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 +
*Person A argues that P
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*Circumstance Q has happened to person P
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*Therefore P is true
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For example: "Yes, [[police|officer]], I realize I was speeding, but you shouldn't give me a ticket because I was racing to see my wife who is in the [[hospital]]." While this argument uses an emotional appeal to convince the officer not to hand out a citation, there is no logical connection between the premise ("you shouldn't give me a ticket") and the conclusion ("I was racing to see my wife").
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 +
===''Argumentum ad hominem''===
 
: ''Main Article: [[Ad hominem]]''
 
: ''Main Article: [[Ad hominem]]''
  
([[Latin]]: "Argument directed toward the man"); An argument that attacks the character of one holding a contrary view, rather than attacking the view itself. ''Name-calling'' is a particularly crude form of this fallacy. ''Argumentum ad hominem'' is usually an attempt to accuse the other person of lying without saying so directly, or saying that his premises are somehow incompetent, irrelevant, or immaterial, or simply unreliable because they are self-serving. However, this is not good logic. If one suspects another of lying, then one should attempt to disprove the premises. One can raise a ''suspicion'' of deliberate falsehood on the part of another who has offered deliberate falsehood in the past. But the most that that can accomplish is to suggest that the other person's premises are unreliable and therefore require third-party corroboration.
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''Ad hominem'' arguments (Lat: "argument directed toward the man") fall into two forms: ''ad hominem'' abusive and ''ad hominem tu quoque'' (circumstantial).
  
===Overgeneralization===
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====''Ad hominem'' abusive====
An argument that attempts to apply a principle to circumstances beyond the scope of its original formulation or of any reliable demonstration. The application of [[Isaac Newton]]'s original theory of relative velocity (which is that it was simply additive) to speeds approaching that of light was an overgeneralization, as [[relativity]] would later show.
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An ''ad hominem'' is an argument which tries to disprove another argument by attacking the person who made it, rather than by focusing on the actual logical reasoning. The goal of an ''ad hominem'' argument is usually to take focus off of the actual argument by calling attention to a flaw of the person making it. This form of argument follows the form:
  
Overgeneralization also is the central problem in trying to conclude something about a population from a non-representative sample, or about a larger group from a non-representative subset of that group.
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*Person A argues that P
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*Person A is Q
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*Q is some derogatory description not related to the argument at hand
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*Therefore P is false
  
===Non sequitur===
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For example: "We all know that George beats his wife, so obviously he's wrong when he says that we should vote against this proposition." This is fallacious reasoning because the premise ("George beats his wife") does not have a logical link with the conclusion ("George is wrong").
: ''Main Article: [[Non sequitur]]''
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([[Latin]]: "It does not follow"); An argument which moves from a premise to a conclusion without showing a valid connection.
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====''Ad hominem tu quoque''====
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A ''tu quoque'' argument (Lat: "you're another") is one which argues that, because someone does that which they are arguing against, that person must be wrong. This form of argument follows the form:
  
===Proof by authority===
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*Person A argues that P should not happen
Also known as ''argumentum ab auctoritate'' ([[Latin]] "Argument proceeding from clout"), this is an argument that a person bases on authority, either his own or that of another person, rather than on the merits of the position. When the authority involved is a relevant source who has access to more information about the topic than the people discussing it, then the argument becomes a ''citation.'' However, a valid citation must be in an area of study, research, or mental discipline in which the authority being cited is a recognized [[expert]].
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*Person A does P
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*Therefore Person A's argument is incorrect
  
A classic example of argument from authority is a reference to a celebrity or religious leader for their opinion on a matter of science or public policy, when that celebrity or cleric has never adequately studied the subject. This kind of argument also appears in commercial advertising or political electioneering.
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For example: "You can't tell me not to eat cheeseburgers, I just saw you eating one last week!" Another common example is often found in business: "why are you punishing me for dumping waste in the river? My opponent does the exact same thing and you don't punish him!" In this case, dumping waste into the river is wrong (and illegal) regardless of how it is enforced for any other company.
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===Genetic fallacy===
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In general, this is the attempt to assert or reject a theory by citing its origins as either reputable or disreputable. The usual expression of this fallacy is "consider the source!" Thus it becomes a form either of ''argumentum ab auctoritate'' or of ''argumentum ad hominem'', depending on whether one seeks to verify or disprove the theory by this method. This type of argument follows the form:
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 +
*If P then Q
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*Q is true
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*P is false
 +
*Therefore Q is false
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 +
When the origin of ''evidence'' or of ''premises'' is relevant to the reliability of the same, then asking a hearer to "consider the source" is valid. Judges in courts of [[law]], for example, routinely reject as unreliable the testimony of any witness who has demonstrably lied about a point that matters in the case at hand. The facts that such a witness is asserting might still be true, but they cannot stand without corroboration from another, more reliable witness.
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But when corroboration is established, the origins of a conclusion, however tainted, become irrelevant.
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As an example, [[Gregor Mendel]] established the genetic theory that remains current today, even though Mendel's experimental technique was badly flawed, and he even stands accused of falsifying key data. But succeeding [[science|scientists]], using accepted methods of verification and statistical assessment, have achieved results consistent with this theory. Thus the theory remains valid even though Mendel's original presentation was fraudulent. Any attempt today to discredit Mendel's theory on account of Mendel's sloppy methods would be an example of a genetic fallacy.<ref name=Genetic>[http://www.fallacyfiles.org/genefall.html Genetic Fallacy] on [http://www.fallacyfiles.org/ The Fallacy Files]</ref>
  
 
===Proof by numbers===
 
===Proof by numbers===
This is an argument that a person bases on the numbers of people holding to its conclusion, rather than on the premises that might support that conclusion. "Ninety nine point nine percent of all respondents can't be wrong" is the classic phraseology. One does not effectively disprove such an argument by challenging the numbers. Instead, one reminds the other person that the numbers of people holding to any given conclusion are irrelevant to establishing the truth or falsehood of that conclusion. [[History]] is in fact replete with multiple examples, too many to mention here, of conclusions that memorable [[science|scientists]] and other great discoverers have shown to be false even though large numbers of people believed them. [[Antoine Lavoisier]], who disproved "phlogiston" as the principle of fire, was one such person. [[Christopher Columbus]] and [[Ferdinand Magellan]] make two more.
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Also known as "appeal to the people" (Lat: ''ad populum''), this is an argument that a person bases on the numbers of people holding to its conclusion, rather than on the premises that might support that conclusion. An appeal to the people follows the form:
  
===Proof by assertion===
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:Most people believe P
An argument that states something as true without offering supporting evidence or attempting to construct a valid argument. The typical form of this "argument" is the "conclusion" of a [[non sequitur]].
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:Therefore P is true
  
===Circular reasoning===
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"Ninety nine point nine percent of all respondents can't be wrong" is the classic phraseology of this fallacy One does not effectively disprove such an argument by challenging the numbers. Instead, one reminds the other person that the numbers of people holding to any given conclusion are irrelevant to establishing the truth or falsehood of that conclusion. [[History]] is in fact replete with multiple examples of conclusions that memorable [[science|scientists]] and other great discoverers have shown to be false even though large numbers of people believed them. [[Antoine Lavoisier]], who disproved "phlogiston" as the principle of fire, was one such person. [[Christopher Columbus]] and [[Ferdinand Magellan]] are two others.
[[Circular reasoning]] is a form of proof-by-assertion in which one asserts a premise, then asserts a conclusion from that premise (directly or indirectly), and then tries to show that the last conclusion ''supports'' the original premise.
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===Special pleading===
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: ''Main Article: [[Special pleading]]''
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[[Special pleading]] means applying to other people a set of standards that one is not willing to apply to oneself, without offering sufficient grounds, called the ''relevant difference'', to support such exemption. Special pleading follows the form:
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 +
*If Person X is in set P then Q happens to person X
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*Person A is in set P
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*Person A cites R circumstance, unrelated to P or Q
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*Therefore Person A is not subject to Q
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 +
For example: a political or military leader who urges his subjects (or those under his command) to observe "iron rations" without similarly depriving himself leaves himself open to a charge of special pleading.
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==Fallacies of Defective or Weak Induction==
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Fallacies of defective or weak induction are fallacies which are due to a lack of understanding for how well premises lead to a conclusion.
  
 
===Argument from silence===
 
===Argument from silence===
Argument from silence (in [[Latin]], ''argumentum ab silencio'') is an assertion that a proposition is false merely because no one has yet asserted evidence to confirm it--or that a proposition is true merely because no one has yet asserted evidence to contradict it. "The absence of evidence does not constitute evidence of absence." The charge of argument from silence applies in a situation in which ''no reasonable attempt has yet been made'' to develop evidence to confirm or contradict the proposition in question.
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''Argument from silence'' (in [[Latin]], ''argumentum ab silencio'') or ''argument from ignorance'' (Lat: ''ad ignorantium'') is an assertion which states that, because there is no evidence to support a given argument, the opposite must be true. The fallacy follows the form:
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*If P then Q
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*P cannot be shown true
 +
*Therefore Q is false
  
This is the opposite extreme from "manufacturing facts to support a theory," described below. The best aid to striking a balance that avoids these two opposing fallacies is [[Occam's razor]].
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For example: "Nobody has ever seen God, so clearly he doesn't exist".
  
===Proving too much===
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This fallacy is often associated with and best remembered by the phrase: "the absence of evidence does not constitute evidence of absence."
A form of overgeneralization in which one attempts to use a set of premises to sustain more conclusions than he can reasonably sustain using the argument presented.
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===Double standard===
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===False cause===
The unequal use of a criterion, and its different application in different cases. This is actually a form of [[hypocrisy]].
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False cause (Lat: ''non causa pro causa'') is a fallacy which arises when a poor cause/effect link is used within an argument, especially if coincidence or chance are not taken into account. The fallacy follows the form:
  
===Your theory does not work under my theory, so your theory must be wrong===
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*P causes Q (faulty reasoning)
: ''Main article: [[Your theory does not work under my theory, so your theory must be wrong]]''
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*P is true
 +
*Therefore Q is true
  
The judgment of a theory by the premises and assumptions of another theory, rather than against its own premises and assumptions. This is a variation on proof-by-assertion.
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For example: "I used to be a well paid teacher until I started being a tougher grader. When my students' grades went down, so did my salary." While this sounds like a logical explanation, not all factors are taken into account. For example, the teacher's school could have been subject to budget cuts, or maybe the teacher was overpaid at first and now his salary corrects his true worth.
  
===Manufacturing facts from a theory===
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====''Post hoc ergo propter hoc''====
: ''Main article: [[Manufacturing facts from a theory]]''
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''Post hoc ergo propter hoc'' (Lat: "after the thing, therefore because of the thing") is a subcategory of false cause fallacies. In this type of argument, a close temporal proximity is used as a justification of a cause/effect relationship. ''Post hoc ergo propter hoc'' arguments follow the form:
  
The assertion as fact of an undemonstrated, unobserved idea for no better reason than that a given theory requires that fact. We deal here with the assumption of a fact ''not in evidence.'' In the early stages of formulating a model, this sort of behavior is acceptable. But when repeated efforts to demonstrate such a new fact ''have failed'', the proper logical response is to discard or revise the theory, and not merely to assume that the "fact" still exists and "someone hasn't tried hard enough" to find it. This is ''especially'' true when someone develops evidence that the inferred "fact" ''could not possibly exist.''
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*P happened, and then Q happened
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*Therefore P caused Q
  
This is yet another form of proof-by-assertion, and is the source of many controversies in modern [[astronomy]], some of them strikingly bitter.
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For example: "Right around the time the sun goes up my alarm clock goes off, so the sun causes my alarm clock to go off." Clearly this is not the case.
  
===Genetic fallacy===
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===Non sequitur===
In general, this is the attempt to aver (that is, assert as true) or reject a theory by citing its origins as either reputable or disreputable. The usual expression of this fallacy is "Consider the source!" Thus it becomes a form either of ''argumentum ab auctoritate'' or of ''argumentum ad hominem'', depending on whether one seeks to verify or disprove the theory by this method.
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: ''Main Article: [[Non sequitur]]''
  
When the origin of ''evidence'' or of ''premises'' is relevant to the reliability of the same, then asking a hearer to "consider the source" is valid. Judges in courts of [[law]], for example, routinely reject as unreliable the testimony of any witness who has demonstrably lied about a point that matters in the case at hand. The facts that such a witness is asserting might still be true, but they cannot stand without corroboration from another, more reliable witness.
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A ''non sequitur'' (Lat: "It does not follow") is an argument which moves from a premise to a conclusion without showing a valid connection, or sometimes any connection at all. This form of argument follows the form:
  
But when corroboration is established, the origins of a conclusion, however tainted, become irrelevant.
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*P
 +
*Therefore R is true
  
As an example, [[Gregor Mendel]] established the genetic theory that remains current today, even though Mendel's experimental technique was badly flawed, and he even stands accused of falsifying key data. But succeeding [[science|scientists]], using accepted methods of verification and statistical assessment, have achieved results consistent with this theory. Thus the theory remains valid even though Mendel's original presentation was fraudulent. Any attempt today to discredit Mendel's theory on account of Mendel's sloppy methods would be an example of a genetic fallacy.<ref name=Genetic>[http://www.fallacyfiles.org/genefall.html Genetic Fallacy] on [http://www.fallacyfiles.org/ The Fallacy Files]</ref>
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For example: "Crime rates are high, so we should increase the penalty for drug possession."
  
===Tautology===
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===Overgeneralization===
A [[tautology]] ([[Greek]] '''ταυτα''' ''tauta'', "these") is an argument that becomes a repetition of a definition. Literally it means "the study of this" or "the study of these." Such an argument, or statement, can prove nothing beyond itself and is useless as a premise.
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Overgeneralization (also called hasty generalization or converse accident) is an error in reasoning which comes about by making a logical leap far greater than what the data allows. Overgeneralization follows the form:
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*P is Q
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*P is in R
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*Therefore R is Q
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For example: "I just read that three kids were arrested yesterday for drug possession. Teens in this country are really going downhill!"
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Overgeneralization the central problem in trying to conclude something about a population from a non-representative sample, or about a larger group from a non-representative subset of that group.
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 +
====Proving too much====
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Proving too much is a form of overgeneralization in which one attempts to use a set of premises to sustain more conclusions than he can reasonably sustain using the argument presented.
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 +
===Proof by authority===
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Also known as ''argumentum ab auctoritate'' ("argument proceeding from clout") or ''argumentum ad verecundiam'' ("appeal to unqualified authority"), this is an argument that a person bases on authority, either his own or that of another person, rather than on the merits of the position. When the authority involved is a relevant source who has access to more information about the topic than the people discussing it, then the argument becomes a ''citation.'' However, a valid citation must be in an area of study, research, or mental discipline in which the authority being cited is a recognized [[expert]].
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*P says Q
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*P is an authority in his field
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*Therefore Q is true
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A classic example of argument from authority is a reference to a celebrity or religious leader for their opinion on a matter of science or public policy, when that celebrity or cleric has never adequately studied the subject. This kind of argument also often appears in commercial advertising or political electioneering.
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==Fallacies of Presumption==
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Fallacies of presumption are fallacies in which an unstated or shaky presumption is made.
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===Accident===
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The fallacy of accident occurs when a generalization is inappropriately applied to an individual. A fallacy of accident follows the form:
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*Some P are Q
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*R is in P
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*Therefore R is Q
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 +
For example: "You are from [[Ohio]], which is a [[red state]], so you must be a [[Republican]]".
  
 
===Contradiction===
 
===Contradiction===
A [[contradiction]] is a statement that contradicts its own terms. [[Aristotle]] famously stated that contradictions cannot exist. In any case of a contradition, some of the premises must be false.
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:''Main article: [[Contradiction]]''
  
Contradictions normally form part of a proof by ''exclusion''. But contradictory arguments are some of the most common flawed arguments, and are closely akin to double standards (see above).
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A contradiction is a statement that contradicts its own terms. [[Aristotle]] famously stated that contradictions cannot exist. In any case of a contradiction, some of the premises must be false. A contradiction is an argument which includes in its reasoning:
  
===Conflation===
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*P
[[Conflation]] is the treatment of two different concepts as one. The most common form of conflation informs the proverbial accusation, "You are comparing apples to oranges."
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*Not P
  
 
===Loaded question===
 
===Loaded question===
 
: ''Main Article: [[Loaded question]]''
 
: ''Main Article: [[Loaded question]]''
  
A [[loaded question]] is a question that assumes facts, usually unflattering, that are not in evidence, with the intent of trapping the other person into admitting those facts. The classic loaded-question example is "When did you stop beating your wife?" Another example is, "Do you disbelieve in [[global warming]], which 99.9 percent of all reputable scientists now accept?" (It is also an example of proof by numbers of adherents.)
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A [[loaded question]] is a question that assumes facts, usually unflattering, that are not in evidence, with the intent of trapping the other person into admitting those facts. The classic loaded-question example is "When did you stop beating your wife?" Another example is, "Do you disbelieve in [[global warming]], which 99.9 percent of all reputable scientists now accept?"
  
===Special pleading===
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===Proof by assertion===
: ''Main Article: [[Special pleading]]''
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Proof by assertion is an argument that states something as true without offering supporting evidence or attempting to construct a valid argument. This form of argument follows the form:
  
[[Special pleading]] means applying to other people a set of standards that one is not willing to apply to oneself, without offering sufficient grounds, called the ''relevant difference'', to support such exemption. Special pleading is a special case of the double standard, and is one of the most despicable forms of hypocrisy. A political or military leader who urges his subjects (or those under his command) to observe "iron rations" without similarly depriving himself leaves himself open to a charge of special pleading.
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*P is true
  
== Related examples of improper reasoning ==
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Often the argument is simply repeated over and over, and no evidence for support is given.
The following categories of poor reasoning are difficult to classify; some might not wish to classify them as logical fallacies ''per se'', but they are still, in most cases, indefensible:
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===Infinite regression===
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Proof by assertion can also be broken down into several subcategories of fallacies: circular reasoning, infinite regression, manufacturing facts from a theory, and your theory does not work under my theory, so your theory must be wrong.
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 +
====Circular reasoning====
 +
:''Main article: [[Circular reasoning]]''
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 +
[[Circular reasoning]], also called begging the question (Lat: petitio principii), is a form of proof by assertion in which one asserts a premise, then asserts a conclusion from that premise (directly or indirectly), and then tries to show that the last conclusion ''supports'' the original premise.
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====Infinite regression====
 
: ''Main Article: [[Infinite regression]]''
 
: ''Main Article: [[Infinite regression]]''
An [[infinite regression]] results when one asserts that a given event caused another, and yet that first event requires another, identical event, to cause ''it.'' [[Panspermia]], an alternative to [[abiogenesis]] as a proposition about the origin of life, suffers from the infinite-regression flaw so long as it fails to state positively what conditions could have brought about an origin of life on a planet other than the earth, ''other than'' the alleged mechanism of the "seeding" of life on the earth itself.
 
  
Is infinite regression ever defensible? If so, when? A [[Conservapedia:Is infinite regression ever valid as a form of reasoning, or acceptable as a way the universe works, or came to be?|debate]] on this issue is now underway.
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An infinite regression results when one asserts that a given event caused another, and yet that first event requires another, identical event, to cause ''it.'' An infinite regression follows the form:
  
== Logical fallacy and the educational establishment ==
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*P<sub>1</sub> causes Q<sub>1</sub>
Today, logic is offered as an elective in [[college]], not as a requirement. Various graduate-school admissions councils (among them the [http://www.mba.com/ Graduate Management Admissions Council] and the [http://www.lsac.org/ Law School Admissions Council]) have long recognized this fact and today test specifically for an appplicant's ability to [[Critical thinking|think critically]] and apply logic.
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*Q<sub>2</sub> causes P<sub>1</sub>
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*P<sub>3</sub> causes Q<sub>2</sub>
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*Q<sub>4</sub> causes P<sub>3</sub>
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*And so on, forever
  
Thus the major admissions tests (Graduate Management Admission Test and Law School Admissions Test) feature questions on logical reasoning. A typical question would present an argument and ask either:
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For example: [[Panspermia]], an alternative to [[abiogenesis]] as a proposition about the origin of life, suffers from the infinite-regression flaw so long as it fails to state positively what conditions could have brought about an origin of life on a planet other than the earth, ''other than'' the alleged mechanism of the "seeding" of life on the earth itself.
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 +
====Manufacturing facts from a theory====
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Manufacturing facts from a theory is the assertion as fact of an undemonstrated, unobserved idea for no better reason than that a given theory requires that fact.
 +
 
 +
In the early stages of formulating a model, this sort of behavior is acceptable. But when repeated efforts to demonstrate such a new fact have failed, the proper logical response is to discard or revise the theory, and not merely to assume that the "fact" still exists and someone hasn't tried hard enough to find it. This is especially true when someone develops evidence that the inferred "fact" could not possibly exist.
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 +
====Your theory does not work under my theory, so your theory must be wrong====
 +
: ''Main article: [[Your theory does not work under my theory, so your theory must be wrong]]'' <!-- note: a Google search for this phrase show that it is exclusive to CreationWiki (well, and now Conservapedia) -->
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 +
This fallacy occurs when one theory is judged by the premises and assumptions of another theory, rather than against its own premises and assumptions. This form of fallacy follows the form:
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 +
*Theory A says that if P then Q
 +
*Theory B says that if P then R
 +
*Therefore theory A is wrong
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 +
For example: "Dinosaurs died 65,000,000 years ago, so the earth couldn't have been created 6,000 years ago."
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 +
===Straw man===
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:''Main article: [[Straw man fallacy]]
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 +
A straw man fallacy occurs by first incorrectly attributing an argument to someone, disproving this argument, then claiming that the person was wrong. A straw man argument follows the form:
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 +
*If P then Q
 +
*Person A says P
 +
*Therefore Q
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 +
Straw man arguments can sometimes be hard to detect, because a valid statement may be used in a distorted fashion. For example:
 +
 
 +
*Person A believes that a military program should be cut
 +
*Person B argues that since Person A wants to cut military funding, he wants to leave the country defenseless to attack
 +
 
 +
This is fallacious reasoning, because there is no way to know ''why'' person A believes what he does, and Person B has used one reason which suits his own purpose. For example, it's quite possible that Person A wants to cut the program because he wants to change the funding to something which he thinks does a ''better'' job at defending the country.
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===Tautology===
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:''Main article: [[tautology]]''
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 +
A [[tautology]] ([[Greek]] '''ταυτα''' ''tauta'', "these") is an argument that becomes a repetition of a definition. Literally it means "the study of this" or "the study of these." Such an argument, or statement, can prove nothing beyond itself and is useless as a premise.
 +
 
 +
==Fallacies of Ambiguity==
 +
Fallacies of ambiguity are fallacies which arise from ambiguity in language used.
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 +
===Amphiboli===
 +
Amphiboli is an ambiguity which arises though loose or awkward phrasing:
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 +
For example: "Save soap and waste paper".
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 +
===Composition===
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The fallacy of composition occurs when the parts of a whole are incorrectly used to describe the whole.
 +
 
 +
For example: "Since one of the battleships is ready to deploy, the whole fleet is ready to deploy".
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 +
===Conflation===
 +
:''Main article: [[Conflation]]''
 +
 
 +
Conflation is the treatment of two different concepts as one.
 +
 
 +
For example: "Comparing apples to oranges".
 +
 
 +
===Division===
 +
The fallacy of division occurs when it is argued that what is true for the whole must be true for its parts.
 +
 
 +
For example: "That company is very important. Since Joe works at that company, he must be very important."
 +
 
 +
===Equivocation===
 +
Equivocation is the use of word with multiple meanings, and then using a different meaning in the conclusion than in the premise.
 +
 
 +
For example: "The coach said we should eat light, so take your heavy coat off."
  
# What the argument assumes,
 
# What sort of evidence, if established, would significantly strengthen (or weaken) the argument, or
 
# Why the argument, as presented, is flawed.
 
  
Still other questions present arguments and then ask the test-taker what reasonable conclusions one might draw from them. Occasionally they present sets of two facts that might seem to contradict one another and ask the test-taker to explain how both facts can be true at once.
 
  
Many of the arguments presented (the ''stimuli'') and the wrong answer choices offered illustrate classic logical fallacies, often strikingly. Examples of ''argumentum ad hominem'' and the closely related fallacy of ''non sequitur'', to name two key errors, abound in these questions.
 
  
Yet for all this effort in trying to identify weaknesses in critical thinking, colleges tend to discourage critical thinking in other ways, mainly in that [[professor]]s often commit the very sort of logical fallacies that these tests, for example, challenge their test-takers with.
 
  
 
== Related References ==
 
== Related References ==
Line 127: Line 278:
 
*[http://www.creationsafaris.com/crevbd.htm The Baloney Detector]
 
*[http://www.creationsafaris.com/crevbd.htm The Baloney Detector]
 
*[http://www.theskepticsguide.org/logicalfallacies.asp SGU-Top 20 Fallacies]
 
*[http://www.theskepticsguide.org/logicalfallacies.asp SGU-Top 20 Fallacies]
 +
*"The Fine Art of Baloney Detection."  Sagan, Carl.  ''The Demon-Haunted World, Science As a Candle in the Dark.'' Ballantine: New York, 1996; pp 201-218.
  
 
== See Also ==
 
== See Also ==
"The Fine Art of Baloney Detection."  Sagan, Carl.  ''The Demon-Haunted World, Science As a Candle in the Dark.'' Ballantine: New York, 1996; pp 201-218.
+
*[[Conservapedia:Is infinite regression ever valid as a form of reasoning, or acceptable as a way the universe works, or came to be?]]
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[[Category:Logic]]

Revision as of 05:00, March 28, 2008

A logical fallacy is an error in logical reasoning. While the common usage of the word fallacy would include any error in reasoning, in logic a fallacy is defined at a particularly deceptive argument which seems correct, but upon further examination is found to be incorrect.[1]

Logical fallacies fall into two general categories: formal fallacies and informal fallacies. Formal fallacies apply to deductive arguments, and are those which relate to an improper application of a rule, whereas informal fallacies apply to inductive arguments, and are those which involve the improper use of the content of an argument.

A logical fallacy is not the same as lying. A lie in logic is a premise that one offers while knowing that it is false.

There are four general categories of fallacies: fallacies of relevance, fallacies of defective or weak induction, fallacies of presumption, and fallacies of ambiguity.

Fallacies of Relevance

Fallacies of relevance are fallacies which are due to a lack of a relevant logical connection between premise and conclusion.

Appeal to force

An appeal to force (Lat: argumentum ad baculum) is an argument which uses a threat of violence or force as a justification for the conclusion. An appeal to force argument follows the form:

  • If person A does not accept P, then Q
  • Q is a threat of force
  • Therefore P is true

For example: "If you do not pay me $30 I will break your leg. Therefore you owe me $30."

Appeal to pity

Also called emotional appeal, (Lat: ad misericordiam) this fallacy is characterized by a use of emotion as a justification for the conclusion. An appeal to pity follows the form:

  • Person A argues that P
  • Circumstance Q has happened to person P
  • Therefore P is true

For example: "Yes, officer, I realize I was speeding, but you shouldn't give me a ticket because I was racing to see my wife who is in the hospital." While this argument uses an emotional appeal to convince the officer not to hand out a citation, there is no logical connection between the premise ("you shouldn't give me a ticket") and the conclusion ("I was racing to see my wife").

Argumentum ad hominem

Main Article: Ad hominem

Ad hominem arguments (Lat: "argument directed toward the man") fall into two forms: ad hominem abusive and ad hominem tu quoque (circumstantial).

Ad hominem abusive

An ad hominem is an argument which tries to disprove another argument by attacking the person who made it, rather than by focusing on the actual logical reasoning. The goal of an ad hominem argument is usually to take focus off of the actual argument by calling attention to a flaw of the person making it. This form of argument follows the form:

  • Person A argues that P
  • Person A is Q
  • Q is some derogatory description not related to the argument at hand
  • Therefore P is false

For example: "We all know that George beats his wife, so obviously he's wrong when he says that we should vote against this proposition." This is fallacious reasoning because the premise ("George beats his wife") does not have a logical link with the conclusion ("George is wrong").

Ad hominem tu quoque

A tu quoque argument (Lat: "you're another") is one which argues that, because someone does that which they are arguing against, that person must be wrong. This form of argument follows the form:

  • Person A argues that P should not happen
  • Person A does P
  • Therefore Person A's argument is incorrect

For example: "You can't tell me not to eat cheeseburgers, I just saw you eating one last week!" Another common example is often found in business: "why are you punishing me for dumping waste in the river? My opponent does the exact same thing and you don't punish him!" In this case, dumping waste into the river is wrong (and illegal) regardless of how it is enforced for any other company.

Genetic fallacy

In general, this is the attempt to assert or reject a theory by citing its origins as either reputable or disreputable. The usual expression of this fallacy is "consider the source!" Thus it becomes a form either of argumentum ab auctoritate or of argumentum ad hominem, depending on whether one seeks to verify or disprove the theory by this method. This type of argument follows the form:

  • If P then Q
  • Q is true
  • P is false
  • Therefore Q is false

When the origin of evidence or of premises is relevant to the reliability of the same, then asking a hearer to "consider the source" is valid. Judges in courts of law, for example, routinely reject as unreliable the testimony of any witness who has demonstrably lied about a point that matters in the case at hand. The facts that such a witness is asserting might still be true, but they cannot stand without corroboration from another, more reliable witness.

But when corroboration is established, the origins of a conclusion, however tainted, become irrelevant.

As an example, Gregor Mendel established the genetic theory that remains current today, even though Mendel's experimental technique was badly flawed, and he even stands accused of falsifying key data. But succeeding scientists, using accepted methods of verification and statistical assessment, have achieved results consistent with this theory. Thus the theory remains valid even though Mendel's original presentation was fraudulent. Any attempt today to discredit Mendel's theory on account of Mendel's sloppy methods would be an example of a genetic fallacy.[2]

Proof by numbers

Also known as "appeal to the people" (Lat: ad populum), this is an argument that a person bases on the numbers of people holding to its conclusion, rather than on the premises that might support that conclusion. An appeal to the people follows the form:

Most people believe P
Therefore P is true

"Ninety nine point nine percent of all respondents can't be wrong" is the classic phraseology of this fallacy One does not effectively disprove such an argument by challenging the numbers. Instead, one reminds the other person that the numbers of people holding to any given conclusion are irrelevant to establishing the truth or falsehood of that conclusion. History is in fact replete with multiple examples of conclusions that memorable scientists and other great discoverers have shown to be false even though large numbers of people believed them. Antoine Lavoisier, who disproved "phlogiston" as the principle of fire, was one such person. Christopher Columbus and Ferdinand Magellan are two others.

Special pleading

Main Article: Special pleading

Special pleading means applying to other people a set of standards that one is not willing to apply to oneself, without offering sufficient grounds, called the relevant difference, to support such exemption. Special pleading follows the form:

  • If Person X is in set P then Q happens to person X
  • Person A is in set P
  • Person A cites R circumstance, unrelated to P or Q
  • Therefore Person A is not subject to Q

For example: a political or military leader who urges his subjects (or those under his command) to observe "iron rations" without similarly depriving himself leaves himself open to a charge of special pleading.

Fallacies of Defective or Weak Induction

Fallacies of defective or weak induction are fallacies which are due to a lack of understanding for how well premises lead to a conclusion.

Argument from silence

Argument from silence (in Latin, argumentum ab silencio) or argument from ignorance (Lat: ad ignorantium) is an assertion which states that, because there is no evidence to support a given argument, the opposite must be true. The fallacy follows the form:

  • If P then Q
  • P cannot be shown true
  • Therefore Q is false

For example: "Nobody has ever seen God, so clearly he doesn't exist".

This fallacy is often associated with and best remembered by the phrase: "the absence of evidence does not constitute evidence of absence."

False cause

False cause (Lat: non causa pro causa) is a fallacy which arises when a poor cause/effect link is used within an argument, especially if coincidence or chance are not taken into account. The fallacy follows the form:

  • P causes Q (faulty reasoning)
  • P is true
  • Therefore Q is true

For example: "I used to be a well paid teacher until I started being a tougher grader. When my students' grades went down, so did my salary." While this sounds like a logical explanation, not all factors are taken into account. For example, the teacher's school could have been subject to budget cuts, or maybe the teacher was overpaid at first and now his salary corrects his true worth.

Post hoc ergo propter hoc

Post hoc ergo propter hoc (Lat: "after the thing, therefore because of the thing") is a subcategory of false cause fallacies. In this type of argument, a close temporal proximity is used as a justification of a cause/effect relationship. Post hoc ergo propter hoc arguments follow the form:

  • P happened, and then Q happened
  • Therefore P caused Q

For example: "Right around the time the sun goes up my alarm clock goes off, so the sun causes my alarm clock to go off." Clearly this is not the case.

Non sequitur

Main Article: Non sequitur

A non sequitur (Lat: "It does not follow") is an argument which moves from a premise to a conclusion without showing a valid connection, or sometimes any connection at all. This form of argument follows the form:

  • P
  • Therefore R is true

For example: "Crime rates are high, so we should increase the penalty for drug possession."

Overgeneralization

Overgeneralization (also called hasty generalization or converse accident) is an error in reasoning which comes about by making a logical leap far greater than what the data allows. Overgeneralization follows the form:

  • P is Q
  • P is in R
  • Therefore R is Q

For example: "I just read that three kids were arrested yesterday for drug possession. Teens in this country are really going downhill!"

Overgeneralization the central problem in trying to conclude something about a population from a non-representative sample, or about a larger group from a non-representative subset of that group.

Proving too much

Proving too much is a form of overgeneralization in which one attempts to use a set of premises to sustain more conclusions than he can reasonably sustain using the argument presented.

Proof by authority

Also known as argumentum ab auctoritate ("argument proceeding from clout") or argumentum ad verecundiam ("appeal to unqualified authority"), this is an argument that a person bases on authority, either his own or that of another person, rather than on the merits of the position. When the authority involved is a relevant source who has access to more information about the topic than the people discussing it, then the argument becomes a citation. However, a valid citation must be in an area of study, research, or mental discipline in which the authority being cited is a recognized expert.

  • P says Q
  • P is an authority in his field
  • Therefore Q is true

A classic example of argument from authority is a reference to a celebrity or religious leader for their opinion on a matter of science or public policy, when that celebrity or cleric has never adequately studied the subject. This kind of argument also often appears in commercial advertising or political electioneering.

Fallacies of Presumption

Fallacies of presumption are fallacies in which an unstated or shaky presumption is made.

Accident

The fallacy of accident occurs when a generalization is inappropriately applied to an individual. A fallacy of accident follows the form:

  • Some P are Q
  • R is in P
  • Therefore R is Q

For example: "You are from Ohio, which is a red state, so you must be a Republican".

Contradiction

Main article: Contradiction

A contradiction is a statement that contradicts its own terms. Aristotle famously stated that contradictions cannot exist. In any case of a contradiction, some of the premises must be false. A contradiction is an argument which includes in its reasoning:

  • P
  • Not P

Loaded question

Main Article: Loaded question

A loaded question is a question that assumes facts, usually unflattering, that are not in evidence, with the intent of trapping the other person into admitting those facts. The classic loaded-question example is "When did you stop beating your wife?" Another example is, "Do you disbelieve in global warming, which 99.9 percent of all reputable scientists now accept?"

Proof by assertion

Proof by assertion is an argument that states something as true without offering supporting evidence or attempting to construct a valid argument. This form of argument follows the form:

  • P is true

Often the argument is simply repeated over and over, and no evidence for support is given.

Proof by assertion can also be broken down into several subcategories of fallacies: circular reasoning, infinite regression, manufacturing facts from a theory, and your theory does not work under my theory, so your theory must be wrong.

Circular reasoning

Main article: Circular reasoning

Circular reasoning, also called begging the question (Lat: petitio principii), is a form of proof by assertion in which one asserts a premise, then asserts a conclusion from that premise (directly or indirectly), and then tries to show that the last conclusion supports the original premise.

Infinite regression

Main Article: Infinite regression

An infinite regression results when one asserts that a given event caused another, and yet that first event requires another, identical event, to cause it. An infinite regression follows the form:

  • P1 causes Q1
  • Q2 causes P1
  • P3 causes Q2
  • Q4 causes P3
  • And so on, forever

For example: Panspermia, an alternative to abiogenesis as a proposition about the origin of life, suffers from the infinite-regression flaw so long as it fails to state positively what conditions could have brought about an origin of life on a planet other than the earth, other than the alleged mechanism of the "seeding" of life on the earth itself.

Manufacturing facts from a theory

Manufacturing facts from a theory is the assertion as fact of an undemonstrated, unobserved idea for no better reason than that a given theory requires that fact.

In the early stages of formulating a model, this sort of behavior is acceptable. But when repeated efforts to demonstrate such a new fact have failed, the proper logical response is to discard or revise the theory, and not merely to assume that the "fact" still exists and someone hasn't tried hard enough to find it. This is especially true when someone develops evidence that the inferred "fact" could not possibly exist.

Your theory does not work under my theory, so your theory must be wrong

Main article: Your theory does not work under my theory, so your theory must be wrong

This fallacy occurs when one theory is judged by the premises and assumptions of another theory, rather than against its own premises and assumptions. This form of fallacy follows the form:

  • Theory A says that if P then Q
  • Theory B says that if P then R
  • Therefore theory A is wrong

For example: "Dinosaurs died 65,000,000 years ago, so the earth couldn't have been created 6,000 years ago."

Straw man

Main article: Straw man fallacy

A straw man fallacy occurs by first incorrectly attributing an argument to someone, disproving this argument, then claiming that the person was wrong. A straw man argument follows the form:

  • If P then Q
  • Person A says P
  • Therefore Q

Straw man arguments can sometimes be hard to detect, because a valid statement may be used in a distorted fashion. For example:

  • Person A believes that a military program should be cut
  • Person B argues that since Person A wants to cut military funding, he wants to leave the country defenseless to attack

This is fallacious reasoning, because there is no way to know why person A believes what he does, and Person B has used one reason which suits his own purpose. For example, it's quite possible that Person A wants to cut the program because he wants to change the funding to something which he thinks does a better job at defending the country.

Tautology

Main article: tautology

A tautology (Greek ταυτα tauta, "these") is an argument that becomes a repetition of a definition. Literally it means "the study of this" or "the study of these." Such an argument, or statement, can prove nothing beyond itself and is useless as a premise.

Fallacies of Ambiguity

Fallacies of ambiguity are fallacies which arise from ambiguity in language used.

Amphiboli

Amphiboli is an ambiguity which arises though loose or awkward phrasing:

For example: "Save soap and waste paper".

Composition

The fallacy of composition occurs when the parts of a whole are incorrectly used to describe the whole.

For example: "Since one of the battleships is ready to deploy, the whole fleet is ready to deploy".

Conflation

Main article: Conflation

Conflation is the treatment of two different concepts as one.

For example: "Comparing apples to oranges".

Division

The fallacy of division occurs when it is argued that what is true for the whole must be true for its parts.

For example: "That company is very important. Since Joe works at that company, he must be very important."

Equivocation

Equivocation is the use of word with multiple meanings, and then using a different meaning in the conclusion than in the premise.

For example: "The coach said we should eat light, so take your heavy coat off."



Related References

  1. Copi, Irving M. and Carl Cohen. "Introduction to Logic, 12e". Pearson Education: 2005
  2. Genetic Fallacy on The Fallacy Files

See Also