Linguistics Encyclopedia.pdf

Next, the child applies X-bar theory (see TRANSFORMATIONAL-GENERATIVE
GRAMMAR), according to which each of the major lexical categories, such as N and V,
is the head of a structure dominated by a phrasal node of the same category, in this case
NP and VP. The child only applies X-bar if there is evidence for the higher category in
the data. In the example we are working with, there is evidence for VP, but not for NP.
Since VP is, in turn, dominated by S, the child can now construct the following tree:
Now the child assigns grammatical functions to the syntactic categories in the tree, i.e.
Subject to N, and connects unattached branches to give
Further steps in the process include: (1) the creation and strengthening of phrase-structure
rules; (2) adding new vocabulary with information about grammatical properties and
strengthening existing entries; (3) collapsing of rules, when new rules are added to the
phrase structure when it already has a rule which expands the same category. For
example,
VP→PP and VP→NP
will be collapsed to
The linguistics encyclopedia 332
(see further Ingram, 1989, pp. 316–30).
During the early stages of stringing more than two words together, many children’s
speech lacks grammatical inflections and function words, consisting of strings like cat
drink milk (Yule, 1985, p. 141); this kind of language is known as telegraphic speech
(Brown and Fraser, 1963). Even if children are presented with full sentences to imitate,
they tend to repeat the sentences in telegraphic form.
Children normally begin to acquire grammatical morphemes at the age of around two
years. The most famous study of the acquisition of grammatical morphemes is that of
Berko (1958), who studied the acquisition by English-speaking children of plural -s,
possessive -s, present tense -s, past-tense -ed, progressive -ing, agentive -er, comparative
-er and -est, and compounds. Berko worked with children aged between four and seven