The fundamental notion with reference to which the different syntactical and semantic rules of systems can be explained is that of a notation—in brief, a symbol system where to each symbol corresponds one item in the realm, and to each item in the realm only one symbol in the system. Hence, for instance, a musical score is a character in a notational system only if it determines which performances belong to the work and, at the same time, is determined by each of those performances (Goodman 1976