 A matrix for a propositional logic L is given by (i) a set K of elements, the truth-values, (ii) a non-empty subset \(D\subseteq K\) of designated truth-values, and (iii) operations on the set K, that is, functions from \(n\)-tuples of truth-values to truth-values, that correspond to the connectives of L. A matrix satisfies a formula A under an assignment \(\sigma\) of elements of K to the variables of A if the value of A under \(\sigma\) is a member of D, that is, a designated value. A matrix satisfies a formula if it satisfies it under every assignment \(\sigma\). A matrix for a modal logic M extends a matrix for a propositional logic by adding a unary function that corresponds to the connective \(\Diamond\).