Logical fallacy

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A Logical fallacy is any argument that suffers from a crippling logical flaw.

Formal 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:

1. All undergraduates are human.
2. All sophomores are human.
3. Therefore, all sophomores are undergraduates.

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.

Logical fallacy is not the same as lying. A lie in logic is a premise that one offers, that the one offering the premise knows 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.

The following is a catalog of logical fallacies, with each one given a separate heading, to make them easier to cite in other articles.

Catalog of Logical Fallacies

Template:Fallacy

Use the {{fallacy|type}} template to insert the above warning on a page containing a logical fallacy. Replace the word "type" with the name of the fallacy to link the warning label to the appropriate page.

Argumentum 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.

Overgeneralization

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 Albert Einstein would later show.

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.

Proof by authority

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.

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.

Proof by assertion

An argument which simply states something as true without evidence or argument to support it.

Circular reasoning

Circular reasoning is any attempt to prove something by first asserting it and then trying to "prove" it through any number of intervening conditional statements.

Proving too much

The use of a classification which includes too many things in the classification.

Double standard

The unequal use of a criterion, by applying it differently in different cases.

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

A theory is judged by the premises and assumptions of another theory, rather than being judged against its own premises and assumptions.

Manufacturing facts from a theory

Main article: Manufacturing facts from a theory

An undemonstrated, unobserved idea is stated as fact because it comports with a particular theory.

Genetic fallacy

According to a leading logical fallacy website, "The Genetic Fallacy is the most general fallacy of irrelevancy involving the origins or history of an idea. It is fallacious to either endorse or condemn an idea based on its past—rather than on its present—merits or demerits, unless its past in some way affects its present value. For instance, the origin of evidence can be quite relevant to its evaluation, especially in historical investigations. The origin of testimony—whether first hand, hearsay, or rumor—carries weight in evaluating it.

In contrast, the value of many scientific ideas can be objectively evaluated by established techniques, so that the origin or history of the idea is irrelevant to its value." Genetic Fallacy on The Fallacy Files

Classic examples of the genetic fallacy include the argument that evolution is wrong because Darwin was evil or because Darwin recanted on his death bed (he did not recant, but even if he had, it would still be irrelevant). Another common use of the genetic fallacy in the other direction is to dismiss a young earth creationist argument since the young earth creationist is motivated by his or her interpretation of the Bible.

Tautology

A tautology is a statement that is true under all circumstances, such that the statement carries no meaning.

Contradiction

A contradiction is a statement that contradicts its own terms, such that it is false by logical necessity.

Conflation

Conflation is the logical fallacy of treating two distinct concepts as if they were one.

Loaded question

Main Article: Loaded question

A loaded question is a question that assumes facts not in evidence, with the intent of trapping the other person into admitting those facts. The classic example of a loaded question is "Have you stopped beating your wife?"

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 any reasonable grounds for claiming such exemption. Jesus Christ, of course, had a word for this sort of behavior: hypocrisy.

Logical fallacy and the educational establishment

Today, logic is offered as an elective in college, not as a requirement. Various graduate-school admissions councils (among them the Graduate Management Admissions Council and the Law School Admissions Council) have long recognized this fact and today test specifically for an appplicant's ability to think critically and apply logic.

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:

1. What the argument assumes,
2. What sort of evidence, if established, would significantly strengthen (or weaken) the argument, or
3. Why the argument, as presented, is flawed.

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 professors often commit the very sort of logical fallacies that these tests, for example, challenge their test-takers with.

Related References

• Logical fallacy by CreationWiki
• The Baloney Detector