# Topic: Logic

Errors in the *structure* of an argument: inferences whose flaw is visible from the logical form alone, regardless of whether the individual claims happen to be true.

| Fallacy | Trigger – look for… |
| ------- | ------------------- |
| **[Denying the antecedent](/check/logic/formal_fallacies/denying_the_antecedent.md)** |  A conditional (“If P then Q”) is misused: because P does not hold, Q is denied – even though Q could have another cause. (Checkable form: “If P → Q; not-P → ∴ not-Q”). |
| **[Affirming the consequent](/check/logic/formal_fallacies/affirming_the_consequent.md)** |  A conditional (“If P then Q”) is misused: because Q holds, P is affirmed – even though Q could have another cause. (Checkable form: “If P → Q; Q → ∴ P”). |
| **[Affirmative conclusion from a negative premise](/check/logic/formal_fallacies/affirmative_conclusion_from_negative_premise.md)** |  In a formal categorical inference (especially a syllogism), an *affirmative* conclusion (“all … are …”, “some … are …”) is inferred although at least one premise is *negative* (“no …”, “some … are not”). |
| **[Negative conclusion from affirmative premises](/check/logic/formal_fallacies/negative_conclusion_from_affirmative_premises.md)** |  In a formal categorical inference (especially a syllogism), a *negative* conclusion (“no …”, “some … are not”) is inferred although all premises are *affirmative* (“all … are …”, “some … are …”). |
| **[Fallacy of exclusive premises](/check/logic/formal_fallacies/exclusive_premises.md)** |  In a standard categorical syllogism or comparable form, *all* premises are negative, yet a conclusion is still derived. |
| **[Undistributed middle](/check/logic/formal_fallacies/fallacies_of_distribution/undistributed_middle.md)** |  In a formal categorical inference (especially a syllogism), the *middle term*, which connects the premises, refers only to a part of its class in all occurrences (typically as predicate of “All X are M”, or within an unqualified “Some …” statement), yet is still used as if it can connect the other terms. (Checkable form: “Some C are M; All P are M → ∴ …P, C…”.) |
| **[Illicit process](/check/logic/formal_fallacies/fallacies_of_distribution/illicit_process.md)** |  In a formal categorical inference (especially a syllogism), the major or minor term occurs in a distributed position (whole-class reference) in the conclusion, yet only in an undistributed position in its premise – i.e., the conclusion makes a broader claim about that class than the premise does. (Checkable form: “All P are M; All M are S → ∴ All S are P” – “S” is broader in the conclusion.) |
| **[Fallacies of distribution](/check/logic/formal_fallacies/fallacies_of_distribution/index.md)** |  A categorical inference (especially a syllogism) in which the *distribution* of terms is evidently mishandled but does not clearly match either specific rule above – e.g., several distribution errors at once, or a non-standard form where the middle/major/minor roles are hard to assign (enthymemes with elided premises, multi-premise chains). Fallback entry: if the conditions for *undistributed middle* or *illicit process* are met, use those instead. |
| **[Ambiguous middle term](/check/logic/formal_fallacies/four-term_fallacy/ambiguous_middle.md)** |  In a syllogism, the middle term shifts meaning between premises (equivocation), so it fails to link the other two terms. (A specific form of the four-term fallacy.) |
| **[Four-term fallacy](/check/logic/formal_fallacies/four-term_fallacy/index.md)** |  A syllogism contains four distinct terms instead of exactly three – often because a term is used in two different meanings (equivocation). Count meanings, not words. |
| **[Circular reasoning](/check/logic/formal_fallacies/circular_reasoning.md)** |  A conclusion is supported by a premise that directly or indirectly depends on that same conclusion, including through a chain of claims that loops back to it. |
| **[Existential fallacy](/check/logic/formal_fallacies/existential.md)** |  An *existential* conclusion ("some A are B") drawn from *universal* premises ("all A are B") that do not establish the class actually exists (vacuously true if A is empty). |
| **[Fallacy of division](/check/logic/emergence/division.md)** |  A property of the *whole* is inferred to hold for its *parts* (or a group-level property for individual members) – as if the parts must share the whole's property, without checking whether it is *emergent*. |
| **[Fallacy of composition](/check/logic/emergence/composition.md)** |  A property of the *parts* (components, members) of a system is inferred to hold for the *whole* as well – as if the whole must be the sum of its parts, without checking for emergent or resultant properties. |
| **[Fallacies of emergence](/check/logic/emergence/index.md)** |  A property is transferred between a *whole* and its *parts* (or a group and its members) as if the levels were interchangeable – without checking whether the property *emerges* upon combination. Umbrella/fallback: route to either *fallacy of division* or *composition* if the direction is clear. |

#END.