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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 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 deragatory 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.

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.

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. "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 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. 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 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.

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.

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 often appears in commercial advertising or political electioneering.

False cause

non causa pro causa

Non sequitur

Main Article: Non sequitur

(Latin: "It does not follow"); An argument which moves from a premise to a conclusion without showing a valid connection.

Overgeneralization

Hasty generalization (aka converse accident)

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.

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.

Proving too much

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.

Fallacies of Presumption

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

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.)

Proof by assertion

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.

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

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.

Manufacturing facts from a theory

Main article: Manufacturing facts from a theory

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.

This is yet another form of proof-by-assertion, and is the source of many controversies in modern astronomy, some of them strikingly bitter.

Circular reasoning

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.

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.

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.

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).

Fallacies of Ambiguity

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

Conflation

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."