The meaning of a sentence is determined form its deep structure by means of the rules of semantic component of a grammar. The phonetic form of a sentence is determined from its surface structure by means of the rules of phonological component. Thus, grammar may now be defined as a system of rules for relating pronunciation of a sentence to its meaning. The syntax, or the base, is at the core of the system and generates the infinite number of structures underlying the grammatical sentences of a language. These structures are, in turn, given a semantic and phonetic interpretation by means of the semantic and phonological component of the grammar. The phonological and semantic component are purely interpretative since they do not generate any sentences on their own but rather assign the phonetic and semantic form to the sentences generated by the syntax.
The base comprises of a set of categorial rules as well as of a lexicon. These two combined serve a function similar to that of phrase structure rules of the earlier system of TGG, with minor exceptions. The lexicon includes all the vocabulary in the language and associates with each the syntactic, semantic, and phonological information essential for the correct operation of the rules. This information is termed ‘features’. For instance, the syntactic features for ‘boy’ are: [+ Noun], [+ Count], [+ Common], [+ Animate], and [+ Human]. The categorial rules have two basic functions, namely “they define the system of grammatical relations, and they determine the ordering of elements in deep structures” (Chomsky 1965:123). The categorial rules generate phrase markers with a number of slots to be completed with lexical items. There is a set of features associated with each slot, which features determine the kind of item that can be filled in the slot. For instance, the noun ‘boy’ could be filled in a slot specified as requiring an animate noun, a common noun, a human noun, or a countable noun, however, the very noun would be excluded from slots specified as requiring an abstract noun (e.g. ‘wisdom’) or an uncountable noun (e.g. ‘sugar’). With the aid of syntactic information (features) assigned to the lexicon, the categorial rules permit sentences such as ‘The boy laughed”, while rejecting and defining as ungrammatical non-sentences such as “The boy elapsed”.
To conclude, Standard Theory modifies the original Transformational-Generative Grammar Theory in that it introduces to the system of grammar an additional semantic component represented by a deep and surface structure in a sentence. Moreover, Standard Theory makes a sharp distinction between competence and performance of an ideal speaker-hearer of a language.
Within the framework of Extended Standard Theory, a view that deep structure exists as a distinct level of syntactic structure at which lexical insertion occurs, and which serves as the input to the transformational component is maintained. Nevertheless, the rules of semantic component operate not on deep structures exclusively, as it was the case in Standard Theory, but also on surface structures of sentences.