Formal/Structural Fallacy: Logical Fallacy Family

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Formal/Structural Fallacy

The argument fails because its internal structure does not validly carry the premises to the conclusion.

Entries

12 fallacies in this family.

Quick family question

If the premises were true, would this form still fail to support the conclusion?

Family vs. category

A family is the broad umbrella that gives a fallacy its main home. Categories are the narrower diagnostic tags, so the same fallacy can appear in multiple categories while still belonging to one family.

Affirmative conclusion from a negative premise

Occurs when a syllogism tries to draw a positive conclusion even though one of the premises is negative in a way that cannot support that conclusion.

Formal

Intermediate High school

Affirming a disjunct

Occurs when someone treats an ordinary 'or' as if it were exclusive and concludes that one option must be false because the other is true.

Formal

Advanced Advanced undergraduate

Affirming the consequent

Occurs when someone reasons from 'if A, then B' and then wrongly infers A merely because B is observed.

Formal

Advanced Advanced undergraduate

Begging the question

Occurs when an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises.

Formal

Foundational Middle school+

Denying the antecedent

Occurs when someone reasons from 'if A, then B' and then wrongly infers 'not B' merely because A is absent.

Formal

Advanced Advanced undergraduate

Exclusive premises

Occurs when two negative premises are used in a syllogism even though they fail to establish the positive link the conclusion requires.

Formal

Intermediate High school

Existential fallacy

Occurs when a conclusion assumes that something exists even though the premises never established that any such thing exists.

Formal

Intermediate High school

Four terms fallacy

Occurs when a syllogism seems to use three terms but actually uses four because one term shifts meaning halfway through the argument.

Formal

Intermediate High school

Illicit major

Occurs when a syllogism distributes the major term in the conclusion even though the major premise never distributed it there.

Formal

Intermediate High school

Masked man fallacy

Occurs when two names or descriptions refer to the same thing, but a belief or knowledge context blocks simple substitution and the argument ignores that.

Formal

Intermediate High school

Square logic

Occurs when an argument becomes so internally tangled that its pieces no longer form a coherent chain from premise to conclusion even though it sounds intricate.

Formal

Intermediate High school

Undistributed middle

Occurs when two things are linked to the same broader category and the argument wrongly infers that one of them must therefore be the other.

Formal

Intermediate High school