nsubj

nsubj is a syntactic dependency label used to identify the nominal subject of a clause. In many annotation schemes, the subject is the noun phrase or pronoun that corresponds to the agent or theme of the verb in active voice, and it is connected to the verb by the nsubj relation. The subject typically appears before the main verb in English and often agrees with the verb in number, though cross-linguistic variation exists.

In Universal Dependencies and similar frameworks, nsubj links the main verb of a clause to its subject. There is a related subtype nsubj:pass used for the subject in passive constructions, where the clause’s patient becomes the syntactic subject. For example, in "John loves Mary," John is the nsubj of loves. In the passive counterpart, "Mary was loved by John," Mary is annotated as nsubj:pass of loved. The labeling helps distinguish who or what is performing the action from other argument roles like direct objects (dobj) or oblique modifiers (nmod).

Edge cases include implied subjects in imperatives or pro-drop languages where overt subjects are absent, in which case no nsubj may be present in the annotation. The nsubj relation remains a central concept in dependency grammar for parsing, linguistic description, and information extraction, providing a consistent way to identify core participants of events or states across languages.