Two key issues in the study of idiom are the metaphorical status of idioms (whether or not underlying metaphors are active in the on-line processing of figurative idiomatic expressions) and the compositional status of idioms (whether or not the overall meaning of such expressions is analyzable from internal elements). This study addresses these questions from the perspective of emergent metaphor theory (Sanford, 2012, 2013), arguing that key properties of such expressions − idiosyncrasy of both form and meaning, the potential for idiom to be manipulated in discourse, and diachronic patterns in changes of idiomatic meaning − follow from the status of metaphorical idioms as highly entrenched instances of both conceptual and syntactic mappings. In the case of both types of schema, the interaction of type and token frequency effects predict the metaphoricity and analyzability of idioms.
