The implication-realization model hypothesizes that emotional syntax in music is a product of two expectation systems—one top down, the other bottom up. Syntactic mismatch or conflict in realizations can occur either within each system or between them. The theory argues that interruption or suppression of parametric expectations generated separately by the two systems explains certain types of recurrent aesthetic strategies in melodic composition and accounts for the most common kinds of musical forms (AAA, AAB, ABB, ABC, and ABA).