next up previous contents
Next: Non-inverted sentences Up: Other Constructions Previous: Locative Adverbial Phrases

   
Auxiliaries

Although there has been some debate about the lexical category of auxiliaries, the English XTAG grammar follows [#!mccawley88!#], [#!haegeman91!#], and others in classifying auxiliaries as verbs. The category of verbs can therefore be divided into two sets, main or lexical verbs, and auxiliary verbs, which can co-occur in a verbal sequence. Only the highest verb in a verbal sequence is marked for tense and agreement regardless of whether it is a main or auxiliary verb. Some auxiliaries (be, do, and have) share with main verbs the property of having overt morphological marking for tense and agreement, while the modal auxiliaries do not. However, all auxiliary verbs differ from main verbs in several crucial ways. The restrictions that an auxiliary verb imposes on the succeeding verb limits the sequence of verbs that can occur. In English, sequences of up to five verbs are allowed, as in sentence ((333)).
(332)0(332
(333)
The music should have been being played [for the president] . 

The required ordering of verb forms when all five verbs are present is:

    modal base perfective progressive passive
The rightmost verb is the main verb of the sentence. While a main verb subcategorizes for the arguments that appear in the sentence, the auxiliary verbs select the particular morphological forms of the verb to follow each of them. The auxiliaries included in the English XTAG grammar are listed in Table 20.1 by type. The third column of Table 20.1 lists the verb forms that are required to follow each type of auxiliary verb.


 
Table 20.1: Auxiliary Verb Properties
TYPE LEX ITEMS SELECTS FOR
modals can, could, may, might, will, base form20.1
  would, ought, shall, should (e.g. will go, might come)
  need  
perfective have past participle
    (e.g. has gone)
progressive be gerund
    (e.g. is going, was coming)
passive be past participle
    (e.g. was helped by Jane)
do support do base form
    (e.g. did go, does come)
infinitive to to base form
    (e.g. to go, to come)
 





 
next up previous contents
Next: Non-inverted sentences Up: Other Constructions Previous: Locative Adverbial Phrases
XTAG Project
1998-09-14