In the Introduction to Syntactic Structures, Chomsky (1957: 11) states that the ??central notion in linguistic theory is that of ?linguistic level?. . . such as phonemics, morphology, phrase structure . . . essentially a set of descriptive devices that are made available for the construction of grammars.?? The term ??grammar?? is used here in the usual ambiguous fashion to refer to both the object of study and the linguist?s model of that object. Thus, in chapter 3 (p.18), Chomsky comes back to the issue of levels referring, both to the complexity of languages and the usefulness of theoretical descriptions. A language is an enormously involved system, and it is quite obvious that any attempt to present directly the set of grammatical phoneme sequences would lead to a grammar so complex that it would be practically useless. For this reason (among others), linguistic description proceeds in terms of a system of ??levels of representations??. Instead of stating the phonemic structure of sentences directly, the linguist sets up such ??higher level?? elements as morphemes, and states separately the morphemic structure of sentences and the phonemic structure of morphemes. It can easily be seen that the joint description of these two levels will be much simpler than a direct description of the phonemic structure of sentences.
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