Kasper's (1993) splitting of the mod field into syntactic and
semantic parts is unnecessary in a lexical rule approach. Since the
adjuncts are added directly to the subcat list of the element
they modify, the lexical rules account for the appropriate structure
sharing between the synsem specified in every adjunct's
mod field and the modified ``head''.
In fact, the lexical rule approach to
adjunct modification even eliminates the need for HPSG's
Head-Adjunct Schema (schema 5) and the complex definition of
a semantic head needed for the Semantics Principle (Pollard and
Sag 1994, p. 322) -- adjunctive elements are essentially given the
status of subcategorised elements and the differences in how the
semantics of the different types of adjuncts interacts with the
semantics of the modified phrase are handled directly in the rules.
The verb therefore remains the semantic head of the sentence, and all
phrases with complements and (possibly) adjuncts are licensed by the
Head-Complement Schema.
In Section 3.3.4 it was proposed to divide prepositions into
three types, reflecting their behaviour as strictly a
pseudo-complement, strictly a true adjunct, or a preposition which can
behave as both. In fact, more types are necessary, to capture the
difference between restrictive, operator, and thematic adjuncts. The
relevant piece of the type hierarchy appeared in
Chapter 2 in Figure 2.12 (page
). I will provide representative lexical entries
for each of these types.
The pure pseudo-complement to is shown in d62. This type of preposition adds an effect attribute to the internal semantics associated with a situation (see Section 3.3.2), if compatible with the relation expressed by the modified verb (see Section 3.3.3). The lexical entry need only specify the value of this attribute. Structure sharing between the semantics of the prepositional phrase and the internal value of the situation is specified in the lexical rule bringing out the pseudo-complement modification. This is handled in this way because this aspect of modification remains constant across prepositions of this type. Constraints on the interaction of the preposition with a particular verb will be governed by the type hierarchy, as outlined in Section 3.3.3.
The lexical entry for by, a thematic adjunct, is shown in d64. The sense of by expressed here is that in John broke the lock by hitting it with a hammer. This type of preposition adds a thematic element to the external semantics associated with a situation. As above, the lexical entry need only specify this thematic element and the basic structure of the modified entity, as the appropriate structure sharing between the semantics of the modified verb and the semantics of the preposition is accomplished in the lexical rule. In this case, the thematic element expresses the particular means through which the situation is accomplished. It also expresses an additional constraint that the actor of the embedded VP (the complement of the preposition) be token-identical with the actor in the main situation.
The lexical entry for the beneficiary for, which can behave as both a pseudo-complement and an adjunct, is shown in d63.
This type of preposition adds a thematic element to either the internal or the external semantics associated with a situation, depending on how it is used in a particular utterance, i.e. whether it is used as a pseudo-complement or adjunct. Again, the lexical entry need only specify the thematic element and the basic structure of the modified entity. Either the lexical rule for pseudo-complements or the lexical rule for thematic adjuncts will be applied to incorporate this adjunct into a sentence. Which rule is used determines where the thematic element is attached, and constraints on the them-arg attribute will result in the appropriate entity playing a role in the thematic situation (see Section 2.5.2). This provides a mechanism for structure-sharing a thematic argument with the appropriate semantic element from the verb semantics, regardless of which particular type of modification occurs on a particular use of the preposition. The lexical rule controlling thematic adjunct attachment essentially enforces the constraint in d71, unifying the thematic argument with the index for the situation as a whole, while constraints on the them-arg for pseudo-complement attachment are defined in the semantic relation hierarchy (see Section 3.3.3).
The lexical entry for the restrictive preposition in, as in John ran in the park is shown in d65. This definition follows that of Kasper (1993), specifying the restriction of an index picked out from the verb semantics. The semantic effect of a simple locative adverbial such as in is only to add a restriction on the LOCATION index associated with the situation - in this case, the location of the situation is in (in-place) the park. This restriction is recorded in the restr feature associated with the external semantics of the situation. The union of this restriction with any existing restrictions allows for the possibility of multiple restrictive PPs within a single sentence. Note also that this lexical entry utilises the standard HPSG approach to semantic specification, as the synsem:loc:cont:nuc attribute of the entry specifies the full sit-desc to be associated with the sentence. Thus the lexical rule for restrictive adjuncts will need only to specify the replacement of the semantics associated with the sentence by this sit-desc, in effect allowing this PP to become the semantic head of the sentence. Since this aspect of the semantics will be controlled by the lexical rules, it therefore does not need to be addressed in phrase structure schemata (see Section 3.5.1).
An approximated representation for the durative operator preposition for, as in Peter reads for two hours, is shown in d66. This also follows Kasper's (1993) treatment of operator adverbials. Here the semantic content of the modified VP appears as an argument of the dur-soa, reflecting the behaviour of operator adjuncts as adjuncts which predicate something of the content they modify.
