The encoding of subcategorisation in GB can be characterised in terms of Williams' (Williams, 1980; Williams, 1981a) theory of argument structure. Argument structure (AS) is a level of syntactic description where the arguments of a predicate are collected into a set where each element corresponds to an indexed thematic role, as in (4):
Within the argument structure of a predicate there can be a distinguished position which functions as the `head thematic role' of the argument structure as a whole (Di Sciullo & Williams, 1987). This thematic role is referred to as the `external argument' as it can only be assigned outside the maximal projection of its predicate. Given standard conventions about feature percolation (Lieber, 1980) and the notion `head of a word' (Williams, 1981b; Di Sciullo & Williams, 1987), the index of the external thematic role is passed on to the maximal projection of its predicate as indicated in (5) where the external argument is underlined following Williams' notation.
Information about the remaining thematic roles -- the `internal arguments' -- is available only within the first projection of the predicate. As shown in (6), the thematic index of an internal argument does not percolate to the VP node, but is assigned within the first projection of the predicate. Such assignment is realised under government, i.e. mutual c-command.
The external thematic role is instead assigned outside the maximal projection of the predicate through predication. Predication is stated as a coindexing procedure which relates a predicative phrase with a c-commanding NP at S-structure, as in (7):
The syntactic realisation of thematic roles in argument structure is constrained and secured by the Projection Principle and the -Criterion (Chomsky, 1981):
In general, it is assumed that categorial selection (c-selection) can be derived as the Canonical Structural Realization (CSR) of its semantic category (Chomsky, 1986b). For example, CSR(patient) is NP. Consequently, the claim is made that only semantic selection (s-selection) needs expressing in the lexicon.
- Projection Principle
- Representations at each syntactic level (i.e. LF, and D- and S-structure) are projected from the lexicon, in that they observe the subcategorisation properties of lexical items.
(Chomsky (1981, 29))
- Each argument bears one and only one -role, and each -role
is assigned to one and only one argument.
(Chomsky (1981, 36))
Control with equi verbs is handled syntactically. In brief, the subject of non-finite VPs is structurally represented as the empty category PRO whose relation to its controller is regulated by the binding theory in terms of c-command, as in (8):
|(8)||John wants [PRO to sleep]|
This implies that verbal (clausal) subcategorisation is always expressed in terms of sentences rather than VPs. Note that, unlike most other theories of grammar, sentences are assumed to be the maximal projection of the (I)nflectional (P)hrase introducing verbal morphology (e.g. tense and aspect) in later versions of GB (Chomsky, 1986a), as in (9):
Verbal dependencies arising in expletive and subject raising constructions are also handled syntactically (Chomsky, 1981). For example, a raising verb such as seem subcategorises for a sentence but has no external argument. If the subcategorised clause is non-finite, the subject moves into matrix subject position to satisfy the Case Filter since only a tensed VP can assign nominative case to its subject, as in (10):
|(10)||John seems [t to sleep]|
If the subcategorised clause is finite, the pleonastic element it is inserted in the matrix subject position to satisfy the Extended Projection Principle which in addition to the Projection Principle above requires that all clauses have subjects (Chomsky, 1981), as in (11):
|(11)||___ seems that John sleeps it seems that John sleeps|
Object raising constructions are also viewed as involving sentential subcategorisation. A verb such as believe subcategorises for an infinitive sentence whose subject is assigned case by the matrix verb across sentential boundaries, as in (12), an occurrence described as exceptional case marking (Chomsky, 1986b).
|(12)||Mary believes [ John to be intelligent]|