From a book I wish I’d read sooner. Remember the continuity versus parsimony question? Never mind parsimony for the moment – here’s more on continuity.
“In order to gain the theoretical rigour he wanted [in the field of child language acquisition], Pinker (1984) invoked the theoretical tools of lexical functional grammar. But since these tools were developed to analyse adult language, and since children’s language on the surface does not look like adult language, he had to make the continuity assumption: underneath, the language of children is structured by the same abstract categories and rules as that of adults. This was a mistake. There is not one shred of evidence for the continuity assumption. The reason children’s language does not look like adult language is that it is not like it in terms of the underlying representations involved; children’s language is structured by much weaker and more local linguistic abstractions. Perhaps, then, we should abandon the continuity assumption and instead adopt the developmental assumption that whereas the processes working at different developmental stages are constant, the actual structures and representations involved are different at these different stages.” (Tomasello 2003: 323-324)
Having made this point, Tomasello goes on to discuss how his proposed theory of child language acquisition is construction-based, rather than word (or morpheme) based – acquisition is a process of mastering ‘utterances’ (in his terminology) from a communicative point of view, not a process of establishing the units of a formal grammar:
“This means that we can posit our own kind of continuity in the process of child language acquisition. In this case, however, we are not talking about a continuity in linguistic representations across development, but rather a continuity of the processes by means of which human language users, at all stages of ontogeny, are storing linguistic units of various kinds and at the same time making many kinds of abstractions across them as well.” (Tomasello 2003: 326)
Tomasello, M (2003), Constructing a Language: A Usage-Based Theory of Language Acquisition. Harvard University Press