Fallacies of Logic

A fallacy is a type of argument that may seem to be correct, but on closer examination proves to be incorrect.

• p ⊃ q
• q
• ∴ p

• p ⊃ q
• ~p
• ∴ ~q

• Accident
• Complex question
• Begging the question

A fallacy of presumption in which a generalization is applied to individual cases that it does not govern.

A fallacy of presumption in which one presupposes the truth of a proposition buried in the question.

A fallacy of presumption in which the conclusion is stated or assumed in one of the premises.

• Equivocation
• Amphiboly
• Accent
• Composition
• Division

A fallacy of ambiguity in which two or more meanings for same word or phrase have been confused for each other.

A fallacy of ambiguity in which a grammar problem leads to alternate possible meanings.

A fallacy of ambiguity in which the meaning of a term in the conclusion does not equal its meaning in the premise, because of a change of emphasis.

A fallacy of ambiguity involving a mistaken inference, in which what is true of the parts are taken to be true of the whole.

A fallacy of ambiguity involving a mistaken inference, in which what is true of the whole is taken to be true of the parts.

• Appeal to emotion / appeal to the populace
• Red herring
• Straw man
• Ad hominem
• Appeal to force
• Missing the point

When correct reasoning is replaced by devices calculated to elicit emotional and nonrational support for the conclusion urged.

When correct reasoning is manipulated by the introduction of some event or character that deliberately misleads the audience and thus hinders rational inference.

When correct reasoning is undermined by the deliberate misrepresentation of the opponent’s position.

When correct reasoning about some issue is replaced by an attack upon the character or special circumstances of the opponent.

When reasoning is replaced by threats in the effort to win support or assent.

When correct reasoning is replaced by the mistaken refutation of a position that was not really at issue.

• Argument from ignorance
• Appeal to inappropriate authority
• False cause
• Hasty generalization

When it is argued that a proposition is true on the grounds that it has not been proved false, or when it is argued that a proposition is false because it has not been proved true.

When the premises of an argument appeals to the judgment of some person or persons who have no legitimate claim to authority in the matter at hand.

When one treats as the cause of a thing that which is not really the cause of that thing, often relying (as in the subtype post hoc ergo propter hoc) merely on the close temporal succession of two event.

When one moves carelessly or too quickly from one or a very few instances to a broad or universal claim.

• Fallacies of relevance
• Fallacies of defective induction
• Fallacies of presumption
• Fallacies of ambiguity

Tu quoque is a kind of circumstantial ad hominem attack, used by the speaker to defend himself/herself by essentially saying, “Look who’s talking.”

The bandwagon fallacy is a kind of ad populum (appeal to the populace) fallacy.

Ad misericordiam (appeal to pity) is a kind of ad populum (appeal to the populace) fallacy.

Guilt by association is a kind of abusive ad hominem fallacy.

• Poisoning the well is a kind of circumstantial ad hominem fallacy.
• It is used to suggest that an opponent’s position should be rejected because the opponent has warped judgment in general.
• Ex: Claiming that Tom Cruise’s opinions on any topic should not be trusted because, as a Scientologist, he believes in aliens.

• Appeal to the stick!
• It’s the name of the appeal to force fallacy.

It is a fallacy of equivocation, because the word “small” is relative. A small elephant is still a large animal.

It is not a fallacy. “Gray” is not a relative term, so it means the same thing in both instances of its use here.

It is a fallacy of amphiboly, because its grammatical error gives two possible meanings: either (1) women prefer democrats over men, or (2) women, not men, prefer democrats.

It is a fallacy of amphiboly, because its grammatical error gives two possible meanings: either (1) Dr. Salick and his wife donated money, or (2) Dr. Salick donated his wife and his money to the center.

It is a fallacy of accent, because a change in emphasis can give different meanings, for instance: (1) we should not say bad things about our friends, (2) we may say bad things about other people, but not our friends, or (3) we may write bad things, but not say bad things, about our friends.

It is a fallacy of accent, because words taken out of context have a different emphasis than they do in context.