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
Category
Formal
Breakdowns in deductive structure where the conclusion does not follow from the form.
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
Negative proof fallacy
Occurs when a claim is treated as true because it has not been disproved, or false because it has not been proved.
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