In The emergence of language, it is argued that much of what generative
linguistics has characterized as ‘rules’ in fact can be derived from domain-
general cognitive mechanisms. One example of this perspective is Bates &
Goodman's contribution ‘On the emergence of grammar in the lexicon’,
which Sabbagh & Gelman say offers ‘…a series of compelling arguments
detailing how development and early acquisition shape the subsequent
acquisition of new information.’ The thrust of the argument presented by
Bates & Goodman is that there is no need to posit the existence of an
independent grammar domain, because grammar can be reduced to the
lexicon, which in Bates & Goodman's account, can be acquired using general
purpose mechanisms. One of several major arguments in favour of this
position presented by the authors is that grammar and vocabulary grow at
the same rates in child speech. Thus, the authors argue that the development
of the lexicon and grammar correlate because there is no grammar outside of
the lexicon.