A slot can be occupied by a terminal or a non-terminal category.
The easiest way to define subcategorisation is to refer to traditional complements or to logical arguments of a predicate. In both cases, these subcategorised elements have phrasal instantiations, which must be specified in syntactic terms.
We set up a list of absolutely necessary and uncontroversial non-terminal categories.
Our list is the following: S, VP, NP, PP, AP, ADVP, DETP and XP.
We are aware that other categories are used in the linguistic community, but they seem to be specialisations of existing categories, compensating, in some formalisms, for the lack of restricting features.
Restricting features are at the user's disposal in EAGLES. The variety of features, feature values and feature combinations provides (in association with a category selected from our list of categories) for a very powerful means of expression. In this way, we ensure that any phrasal restriction can be expressed.
As a consequence, our list of categories remains very short. Sentences, for instance, do not have to be split into that-clause, infinitival, interrogative-clause or whatever. In this way, we avoid explosion in the number of categories, which is otherwise mainly due to the mixing of different kinds of information in the category label.
Another consequence is that our list of categories is completely language independent, whereas morphosyntactic features can be very language dependent.
The need for terminal categories is not obvious at first sight. We consider the following cases.
Verb complementation, which is best known, is not concerned with such a specification, except for impersonal subjects. However, the concept of complementation and the need for subcategorisation is not restricted to verbs.
Subcategorisation applies virtually to any entry. As such, major categories like adjective, noun and adverb definitely need subcategorisation specifications.
|(64)||A loaf of bread||(N)|
|(65)||Curious about these things||(ADJ)|
|(66)||Plenty of bread||(ADJ)|
In the long run, minor categories may also be candidates for subcategorisation specifications. For example, some prepositions call for infinitivals, some do not.
We may see `subcategorisation' as nothing else but `lexical selection'. However, this latter notion is much larger than `complementation'. What comes under lexical selection may be:
Subcategorisation may be more or less fine grained. This requirement shows up with the encoding of large scale lexicons only. Some specifications require one to go down to the terminal level, close to phrase rewriting.
For example, some predicative adjectives take an impersonal subject:
|(67)||It is obvious that this subject must be taken into account|
|(68)||Il est évident que nous devons traiter ce sujet|
As the needs for such specifications cannot be settled once and for all (too many lexical units to be considered, too many languages to be handled, too many views on lexicon and subcategorisation), allowing for terminal categories in slot definitions covers such specifications.
When describing complementation patterns, restrictions have to be placed not only on subcategorised elements, but also on the subcategorising element. Some restrictions must be added in a syntactic frame on the lexical unit itself: auxiliary, tense, number and so on. These restrictions are treated in a similar way to restrictions on complements, that is to say by restricting features on a category. Therefore, the lexical unit is pointed to by its terminal category:
|(69)||To go down to the cellar (to have gone down, be down)||(V[Aux:BE])|
|(70)||Descendre à la cave (être descendu)|
|(71)||To go down the steps (to have gone down)||([Aux:HAVE])|
|(72)||Descendre les escaliers (avoir descendu)|
The set of terminal categories which may be entered in a slot derives directly from the list of categories provided by the Morphosyntax group. This guarantees coherence between the different layers of the lexicon in terms of linguistic approach and formal descriptive language and sets up an interface between layers.
For more information on these categorial labels (definition and usage) please refer to the EAGLES CLWG Morphosyntax document. The list of shared categories is the following: noun, adjective, pronoun, verb, adverb, conjunction, adposition, determiner, article and interjection.