In mathematical logic, a Hintikka set is a set of logical formulas whose elements satisfy the following properties:
- An atom or its conjugate can appear in the set but not both,
- If a formula in the set has a main operator that is of "conjuctive-type", then its two operands appear in the set,
- If a formula in the set has a main operator that is of "disjuntive-type", then at least one of its two operands appears in the set.
The exact meaning of "conjuctive-type" and "disjunctive-type" is defined by the method of semantic tableaux.
Hintikka sets arise when attempting to prove completeness of propositional logic using semantic tableaux. They are named after Jaakko Hintikka.