In this paper I review some of the theoretical issues surrounding metaphor, investigating the understanding of metaphor-based constructions from a developmental psycholinguistic view. Reviewing the classification of metaphorical expressions, I elaborate on the morphological aspect of idioms; thus on the typology of metaphors, distinguishing them on the basis of their decomposability and conventionality (Gibbs 1994). I hypothesize a new, mentalistic model of interpretation, in which our mentalizing, intention-reading skills play a key role in deciphering intended (figurative) meaning. Furthermore, I point out the importance of decomposability and conventionality determining our interpretative processes; both factors playing a facilitating role in interpretation.