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Verbs in English that are termed ergative display the kind of alternation shown in the sentences in ((7)) below.
The sun melted the ice .
The ice melted . 

The pattern of ergative pairs as seen in ((7)) is for the object of the transitive sentence to be the subject of the intransitive sentence. The literature discussing such pairs is based largely on syntactic models that involve movement, particularly GB. Within that framework two basic approaches are discussed:

The Derived Intransitive approach's notions of movement in the lexicon or in the grammar are not represented as such in the XTAG grammar. However, distinctions drawn in these arguments can be translated to the FB-LTAG framework. In the XTAG grammar the difference between these two approaches is not a matter of movement but rather a question of tree family membership. The relation between sentences represented in terms of movement in other frameworks is represented in XTAG by membership in the same tree family. Wh-questions and their indicative counterparts are one example of this. Adopting the Pure Intransitive approach suggested by [#!Napoli88!#] would mean placing the intransitive ergatives in a tree family with other intransitive verbs and separate from the transitive variants of the same verbs. This would result in a grammar that represented intransitive ergatives as more closely related to other intransitives than to their transitive counterparts. The only hint of the relation between the intransitive ergatives and the transitive ergatives would be that ergative verbs would select both tree families. While this is a workable solution, it is an unattractive one for the English XTAG grammar because semantic coherence is implicitly associated with tree families in our analysis of other constructions. In particular, constancy in thematic role is represented by constancy in node names across sentence types within a tree family. For example, if the object of a declarative tree is NP1 the subject of the passive tree(s) in that family will also be NP1. The analysis that has been implemented in the English XTAG grammar is an adaptation of the Derived Intransitive approach. The ergative verbs select one family, Tnx0Vnx1, that contains both transitive and intransitive trees. The <trans> feature appears on the intransitive ergative trees with the value - and on the transitive trees with the value +. This creates the two possibilities needed to account for the data.
Figure: Ergative Tree: $\alpha $Enx1V

The declarative ergative tree is shown in Figure 7.1 with the <trans> feature displayed. Note that the index of the subject NP indicates that it originated as the object of the verb.
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XTAG Project