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In passive constructions such as ((181)), the subject NP is interpreted as having the same role as the direct object NP in the corresponding active declarative ((182)).
An airline buy-out bill was approved by the House. (WSJ)  (181)0(181
The House approved an airline buy-out bill. 

ps/passives-files/   ps/passives-files/   ps/passives-files/
(a)   (b)   (c)

{Passive trees in the Sentential Complement with NP tree family: $\beta$nx1Vs2 (a), $\beta$nx1Vbynx0s2 (b) and $\beta$nx1Vs2bynx0 (c)


In a movement analysis, the direct object is said to have moved to the subject position. The original declarative subject is either absent in the passive or is in a by headed PP (by phrase). In the English XTAG grammar, passive constructions are handled by having separate trees within the appropriate tree families. Passive trees are found in most tree families that have a direct object in the declarative tree (the light verb tree families, for instance, do not contain passive trees). Passive trees occur in pairs - one tree with the by phrase, and another without it. Variations in the location of the by phrase are possible if a subcategorization includes other arguments such as a PP or an indirect object. Additional trees are required for these variations. For example, the Sentential Complement with NP tree family has three passive trees, shown in Figure 13.1: one without the by-phrase (Figure 13.1(a)), one with the by phrase before the sentential complement (Figure 13.1(b)), and one with the by phrase after the sentential complement (Figure 13.1(c)). Figure 13.1(a) also shows the feature restrictions imposed on the anchor13.1. Only verbs with <mode>=ppart (i.e. verbs with passive morphology) can anchor this tree. The <mode> feature is also responsible for requiring that passive be adjoin into the tree to create a matrix sentence. Since a requirement is imposed that all matrix sentences must have <mode>=ind/imp, an auxiliary verb that selects <mode>=ppart and <passive>=+ (such as was) must adjoin (see Chapter 21 for more information on the auxiliary verb system).

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