I have proposed four mechanisms that acquire lexical entries: L1, L2, L4, and L5 (recall that L3 acquires the general paradigms used by L4 and L5). These procedures can be organized into a taxonomy that will become useful when we examine the evidence concerning lexical development. The taxonomy, displayed in figure 17 [immagine], classifies the procedures in terms of [...] they are productive or unproductive (i.e., whether they can create subcategorization frames that are not exemplified in the input) [...].
- Pinker (2004), Pag. 253