A quantifier inference rule: if "Most A are B" AND "Most A are C," then "Some A are both B and C." The principle holds because two majorities of the same set must share at least one member — if more than half of A are B and more than half of A are C, the two subsets cannot be disjoint. This is one of the most commonly tested quantifier inferences on LSAT Must Be True / Inference questions and is the only way to derive a "some" claim from two "most" claims.