Frank Van Eynde, Centrum voor Computerlinguïstiek, K.U.Leuven
Typical examples of heads without content are the case marking prepositions of a.o. English and Dutch. Syntactically they take an NP complement to build a PP, but the semantic value of the PP is entirely determined by the NP (cf. GPSG 85). This not only captures the intuition of semantic vacuity, it also provides an explanation for the binding facts in "Mr. Bean (i) sent a postcard to himself(i)/*him(i)" (cf. HPSG 94).
This paper deals with the question of whether such vacuous heads also occur among verbs. A natural candidate is the copula, which in the HPSG 94 analysis indeed passes on the semantic value of its predicative XP complement without adding any semantic content of its own. While intuitively plausible, this analysis does not account for the tense of the copula. Nor does it provide any criteria for the identification of vacuous verbs in general (is the copula the only one?).
To get a handle on these problems I start from the treatment of tense in DRT 93 and propose a way of integrating it in the HPSG 94 notation, refining the representation of the CONTENT values of verbs and defining how they relate to the corresponding CONTEXT values (Van Eynde 98). The resulting analysis provides the means for making a clear distinction between vacuous and non-vacuous verbs, which --when applied to Dutch— shows (1) that the copula is not the only vacuous verb, and (2) that the copula is only vacuous in some of its uses.
In a final section, the observations about case marking prepositions and vacuous verbs will be compared in order to arrive at a general characterization of the notion "head-without-content" (leeghoofd). The relevance of this notion for NLP will be highlighted with examples from machine translation and NL reasoning.
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