Decision procedure
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
Twenty-four out of two hundred and fifty-six
Aristotle's syllogisms are four sentence forms in four arrangements, which makes 256 patterns of argument. Fifteen of them are valid. Nine more become valid if you assume the things being talked about exist, and the gap between those numbers is a two-thousand-year-old disagreement.
The tree that closes
To prove a formula, assume it false and take it apart. Every branch ends in a contradiction, or one of them describes exactly how it could have been false — and either way the tree is the answer, drawn.
Named alongside it
The objects these essays reach for when they reach for this one.
BranchingCategorical statementCompletenessCounterexampleExistential importLiteralProof systemQuantifierRefutationSatisfiabilitySoundnessSyllogism