11.6: Glossary

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Bradley H. Dowden
California State University Sacramento

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antecedent The if-part of a conditional.

conditional An if-then statement.

consequent The then-part of a conditional.

contradictory A logical inconsistency between two statements in which one must be true while the other is false.

contrary A logical inconsistency between two statements when both could be simultaneously false.

fallacy of affirming the consequent A deductive argument of the form "If P then Q; Q; so, P.”

fallacy of denying the antecedent A deductive argument of the form "If P then Q; not-P; so not-Q.”

logical form of a contradiction The statement form "P and not-P."

logically analogous Having the same logical form.

logically equivalent Logically implying each other. Alternatively, we can say two statements are logically equivalent if they are true in the same situations and false in the same situations.

modus ponens A deductive argument of the form "If P then Q; P; so Q.”

modus tollens A deductive argument of the form "If P then Q; not-Q; so not-P."

negation The negation of statement P is a statement of the form "not-P" that is true when P is false and that is false when P is true.

Sentential Logic The branch of logic that focuses on how the logical forms of complex sentences and arguments are composed from the logical forms of their sub-sentences or clauses. The clauses will be connected by one of the following sentence connectors or their synonyms: and, or, not, or if-then. Sentential Logic is also called Propositional Logic and Statement Logic.