  Modern categorical logic as well as the Kripke and topological models of
intuitionistic logic suggest that the interpretation of ordinary
"propositional" logic should in general be the logic of subsets of a given
universe set. Partitions on a set are dual to subsets of a set in the sense of
the category-theoretic duality of epimorphisms and monomorphisms--which is
reflected in the duality between quotient objects and subobjects throughout
algebra. If "propositional" logic is thus seen as the logic of subsets of a
universe set, then the question naturally arises of a dual logic of partitions
on a universe set. This paper is an introduction to that logic of partitions
dual to classical subset logic. The paper goes from basic concepts up through
the correctness and completeness theorems for a tableau system of partition
logic.
