Semantic Extension Schema
Booij's semantic extension schema (Booij 1986) attempts to account for polysemous meanings of affixes without resorting to the Separation Hypothesis. He proposes that the suffix -er, for example, entered Dutch as an Agentive marker. Its meaning then predictably extended to nonanimate Subjects and from there to Instruments, e.g.spel-er 'player' > bijsluit-er 'enclosure' > open-er 'opener'. See Beard (1990) for a response.