Interaction with adjoined Comps

The XTAG analysis now has two different ways of introducing a complementizer like that or for, depending upon whether it occurs in a relative clause or in sentential complementation. Relative clause complementizers substitute in (using the tree Comp), while sentential complementizers adjoin in (using the tree COMPs). Cases like ((260)) where both kinds of complementizers illicitly occur together are blocked.

(259)0(259

(260)

*the book [_w<<15225>>i [that [that [Muriel wrote _i]]]] 

This is accomplished by setting the S_r.t:<comp> feature in the relative clause tree to nil. The S_r.t:<comp> feature of the auxiliary tree that introduces (the sentential complementation) that is set to that. This leads to a feature clash ruling out ((260)). On the other hand, if a sentential complement taking verb is adjoined in at S_r, this feature clash goes away (cf. (261)).

(260)0(260

(261)

the book [_w<<15236>>i [that Beth thinks [that [Muriel wrote _i]]]]