three book is a noun phrase that functions as direct object; poss₁ sister is a noun phrase that functions as subject; buy is the verb. Both noun phrases contain a modifier, the numeral three and the possessive pronoun poss₁ , respectively.

If presented in a bracketed structure (which, however, is not required here), the structure would be as follows (for the sake of simplicity, we treat the possessive pronoun as an adjective):

[ [ [ [three] _Adj ]_AdjP [book]_n ]_np [ [ [ [poss₁] _Adj ]_AdjP [sister]_n ]_np [buy]_v ]_vp ]_s

The order is special since the basic constituent order in ASL is SVO. In this sentence, however, the order is OSV. That is, we are dealing with a marked order. The non-manual marker ‘t’ indicates that this marked order results from topicalization of the object NP.