The paper treats issues concerning the modular modelisation of musical mental processes. Some musical phenomena, like musical illusions, are explained in the framework of modularity and hypotheses are advanced in which the modular model seems very promising for the study of musical perception and cognition. In addition, arguments are proposed to distinguish between levels of abstraction and knowledge in musical cognitive processes.Moreover, some aspects about the theory of musical competence and the theory of musical processing are identified and the possibilities (...) for the integration of varying theoretical assertions are considered in light of these distinctions. (shrink)