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Sentential Subjects
Tree families: Ts0Vnx1, Ts0Ax1, Ts0N1, Ts0Pnx1, Ts0ARBPnx1,
Ts0PPnx1, Ts0PNaPnx1, Ts0V, Ts0Vtonx1, Ts0NPnx1, Ts0APnx1, Ts0A1s1.
Verbs that select sentential subjects anchor trees that have an S node
in the subject position rather than an NP node. Since extraction is
not possible from sentential subjects, they are implemented as
substitution nodes in the English XTAG grammar. Restrictions on
sentential subjects, such as the required that complementizer for
indicatives, are enforced by feature values specified on the S
substitution node in the elementary tree.
Sentential subjects behave essentially like sentential complements, with a few
exceptions. In general, all verbs which license sentential subjects license
the same set of clause types. Thus, unlike sentential complement verbs which
select particular complementizers and clause types, the matrix verbs licensing
sentential subjects merely license the S argument. Information about the
complementizer or embedded verb is located in the tree features, rather than in
the features of each verb selecting that tree. Thus, all sentential subject
trees have the same <mode>, <comp> and <assign-comp> values shown in Figure 8.7(a).
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- {Comparison of $<$assign-comp$>$ values for sentential subjects: $\alpha$s0Vnx1 (a) and sentential complements: $\beta$nx0Vs1 (b)
The major difference in clause types licensed by S-subjs and S-comps is that
indicative S-subjs obligatorily have a complementizer (see examples in
section 8.2). The <assign-comp> feature is used here to
license a null complementizer for infinitival but not indicative clauses. <assign-comp> has the same possible values as <comp>, with the
exception that the nil value is `split' into ind_nil and inf_nil. This difference in feature values is illustrated in
Figure 8.7.
Another minor difference is that whether but not if is
grammatical with S-subjs.8.10 Thus,
if is not among the <comp> values allowed in S-subjs.
The final difference from S-comps is that there are no S-subjs with <mode>=ger. As noted in footnote 4 of
this chapter, gerundive complements are only allowed when there is no
corresponding NP parse. In the case of gerundive S-subjs, there is
always an NP parse available.
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XTAG Project
http://www.cis.upenn.edu/~xtag