fallacy

1. deceptive or false appearance
2. an argument which professes to be decisive, but in reality is not
3. a misconception resulting from incorrect reasoning

1. ad hominem
2. argument from authority ad vericundiam
3. argument from adverse consequences
4. appeal to ignorance ad ignoratium
5. special pleading
6. begging the question
7. observational selection
8. statistics of small numbers
9. misunderstanding the nature of statistics
10. inconsistency
11. non sequitur
12. post hoc, ergo propter hoc
13. meaningless question
14. excluded middle or false dichotomy
15. short-term vs long-term
16. slippery slope
17. confusion of correlation and causation
18. straw man
19. suppressed evidence or half-truths
20. weasel words

(todo: map these to the fallacies of relevance and fallacies of ambiguity. Also, give list of common names for classical fallacies.)

Fal"la*cy (?), n.; pl. Fallacies (#). [OE. fallace, fallas, deception, F. fallace, fr. L. fallacia, fr. fallax deceitful, deceptive, fr. fallere to deceive. See Fail.]

1.

Deceptive or false appearance; deceitfulness; that which misleads the eye or the mind; deception.

Winning by conquest what the first man lost, By fallacy surprised. Milton.

2. Logic

An argument, or apparent argument, which professes to be decisive of the matter at issue, while in reality it is not; a sophism.

Syn. -- Deception; deceit; mistake. -- Fallacy, Sophistry. A fallacy is an argument which professes to be decisive, but in reality is not; sophistry is also false reasoning, but of so specious and subtle a kind as to render it difficult to expose its fallacy. Many fallacies are obvious, but the evil of sophistry lies in its consummate art. "Men are apt to suffer their minds to be misled by fallacies which gratify their passions. Many persons have obscured and confounded the nature of things by their wretched sophistry; though an act be never so sinful, they will strip it of its guilt." South.

© Webster 1913.