Fallacies and uses of language
A fallacy is an error in reasoning: formal if the argument's form is invalid, informal if its content or language misleads. Terms carry denotation and connotation.
Formal fallacies
| Fallacy | What goes wrong |
|---|---|
| Undistributed middle | The middle term is not distributed in either premise. All dogs are mammals; all cats are mammals; so all cats are dogs. |
| Illicit major | The major term is distributed in the conclusion but not in the major premise |
| Illicit minor | The minor term is distributed in the conclusion but not in the minor premise |
| Four terms | A fourth term slips in, often one word used in two senses |
| Affirming the consequent | If P then Q; Q; so P |
| Denying the antecedent | If P then Q; not P; so not Q |
Common informal fallacies
| Fallacy | What it does |
|---|---|
| Ad hominem | Attacks the person instead of the argument |
| Ad populum | Appeals to the crowd or to popularity |
| Ad verecundiam | Appeals to an authority outside their field |
| Ad ignorantiam | True because not proved false (or false because not proved true) |
| Ad baculum | Appeals to force or threat |
| Ad misericordiam | Appeals to pity |
| Straw man | Attacks a distorted version of the opponent's view |
| Begging the question (petitio principii) | Assumes the conclusion in a premise |
| Hasty generalisation | Draws a general rule from too few cases |
| False cause (post hoc) | 'After this, therefore because of this' |
| Equivocation | Shifts the meaning of a word within the argument |
| Amphiboly | Ambiguity from loose grammar or sentence structure |
| Composition / division | Whole judged from its parts / parts judged from the whole |
| Red herring | Diverts attention to an irrelevant issue |
Three basic uses of language
Copi also notes ceremonial language, which mixes these uses, and performative utterances, which perform the act they name (‘I apologise’).
Connotation and denotation of terms
Law of inverse variation: as connotation increases, denotation decreases. Animal → mammal → dog: more attributes, fewer members.
How NET asks this: a short argument is given and you name the fallacy, or you match fallacy names (often Latin) with their descriptions.
Typical MCQ: “'He has been to prison, so his economic theory is wrong.' Which fallacy?” Argumentum ad hominem: it attacks the person, not the argument.
Typical MCQ: “'If it rains, the road gets wet. The road is wet, so it rained.' Which fallacy?” Affirming the consequent, a formal fallacy. The road could be wet for some other reason.
Denotation designates the things; connotation lists the characteristics. Add characteristics and the class shrinks.