Complements and adjuncts have very different structures in the XTAG grammar. Complements are included in the elementary tree anchored by the verb that selects them, while adjuncts do not originate in the same elementary tree as the verb anchoring the sentence, but are instead added to a structure by adjunction. The contrasts between complements and adjuncts have been extensively discussed in the linguistics literature and the classification of a given element as one or the other remains a matter of debate