unaccusativeunergative

Unaccusative and unergative are two classes of intransitive verbs used in linguistic theory to describe how the single argument of an intransitive clause relates to the event and the clause’s syntax. In unaccusative verbs, the subject is not an agent but an internal argument, typically a patient or theme, whose underlying position lies within the verb’s object layer. In unergative verbs, the subject corresponds to an external argument, usually the agent performing the action.

Examples help illustrate the distinction. Unaccusatives include arrive, die, disappear, fall, melt, and grow old: The door opened. The ice melted. Unergatives include run, sleep, laugh, talk, and swim: The dog ran. The children slept. These differences are reflected in how the verbs behave in syntax, particularly with respect to how subjects are formed, how passives can be constructed, and how the verb interacts with functional heads that encode tense, aspect, and voice.

The distinction has played a central role in theories of argument structure and the architecture of the verb phrase. It is closely associated with ideas about external and internal arguments, the location of the subject within the vP/Voice domain, and the conditions under which certain verbs can participate in passive constructions or subject-raising patterns. Burzio’s Generalization and related work connect the presence or absence of an external argument to the lexical semantics of the verb, influencing crosslinguistic patterns of morphology and word order.

Judgments about the clarity of the split vary across languages and contexts. Some verbs are ambiguous, and some languages encode the distinction more transparently than others. Nonetheless, the unaccusative–unergative framework remains a foundational tool for describing intransitive verbs and their syntactic behavior.