There is a variant of the third acquisition mechanism for lexical entries. When a child learns a nonbasic verb form such as a passive, he or she could use a modified version of L3 to note how that form encodes its thematic roles grammatically, and could then generalize that other verbs may map their thematic roles onto grammatical functions in the same way. One can call this the method of "noncanonical mapping" or L5 [...]. Noncanonical mapping [...] requires that a verb have clearly identifiable thematic roles so that these roles can be mapped onto the proper grammatical relations; this would not works for passivizable constructions lacking such roles - for instance, idioms (e.g., "John made headway in his quest for a perpetual motion machine/Not much headway was made yesterday in that quest") - and lexical rules would still be needed for such cases.
- Pinker (2004), a pag.252