HARP (Hybrid Action Representation and Planning), a prototype high-level system for computer-aided composition, is introduced. HARP represents and manipulates music knowledge using a twofold formalism. An object-oriented concurrent environment, the analogical subsystem, provides procedures to manage the sound itself (samples, codes, and algorithms) and particular analysis processes. The symbolic subsystem, a declarative symbolic environment, stores higher level scores, composition rules, definitions in general, and descriptions of pieces of music. The symbolic subsystem is based on a multiple-inheritance semantic network formalism derived from KL-One. The HARP knowledge base, system interface, and reasoning mechanisms are discussed. An important set of analogical descriptions in HARP, based on the metaphor of force fields, is examined. >