Logical Fallacies

Excerpted from "Current Issues & Enduring Questions" by Sylvan Barnet and Hugo Bedau.

Logical fallacies are argumentative moves which basically break the rules of argumentation. They are often thought of as mistakes, errors, and confusions in oral or written discourse. Here is a list of a few of them:

The fallacy of many questions refers to a posed question which can not be simply answered with a yes or no. The questioneer has made too many assumptions in posing the question.

Ambiguity refers to a claim which incorporates wording that gives rise to multiple interpretations, therby confusing the reader.

Death by a thousand qualifications results when a term is used to define something but then there are so many qualifications to the definition as to render the original term meaningless.

Oversimplification occurs when a statement generalizes too much and exaggerates or overstates. In this case, more qualification is needed.

Afalse dichotomyoccurs when an author presents two solutions to a question as mutually exclusive but in reality they are not mutually exclusive. In essence, the author presents a "false choice."

Non sequitur is when one statement seems to necessarily follow another, but the following statement need not logically follow.

The fallacy of composition is when all of the individual components of a group possess a particular characteristic or property that necessarily the group fromed by these components will possess the same characteristic or property.

The fallacy of division is (the reverse of the fallacy of composition) is when a property or characteristic of a collective is necessarily attibuted to an individual member of that collective.

Poisoning the Well occurs when one tries to shift the attention of the reader away from the merits of an argument by drawing attention to the (presumably questionable) source of the argument.

An ad hominem attack is another way of distracting the attention of the reader away from the merits of an argument. In this case, one does it by attacking the man who is responsible for the argument rahter than the argument itself.

The genetic fallacy is when an argument's origin is brought into question as a diversionary tactic rather than the argument itself (related to poisoning the well).

An Appeal to Authority may seen to be misleading when the authoritative figure who is being cited presents no valid reason to believe what he/she is saying other than the fact that he/she is an authoritative person.

The Slippery Slope argument is one which projects a future where a proliferation of similar effects may be witnessed even though there is no compelling reason to believe that this chain of events would likely occur.

The Appeal to Ignorance is one that suggests that because something is unknowable it must not be valid.

Begging the Question is when there are assumptions implicit within a staement that necessarily lead the reader to the author's conclusion.

The False Analogy is whenone makes an analogy between two seemingly similar objects yet the analgoy does not hold because the the two items compared are not similar in all ways.

Post Hoc Ergo Propter Hoc is a Latin phrase that means "after this therefore because of of this". One falls prey to this fallacy when one draws the conclusion about the causation of something because one thing occurs after another.[ Just because one thing occurs after another does not necessarily mean that the first thing caused the second thing.]

The Nizkor Project's guide to logical fallacies [table of contents]