An ergative verb (/ɜ:(r)gətɪv vɜ:(r)b/) or labile verb is a type of ambitransitive verb whose subject when used intransitively corresponds to its direct object when used transitively, meaning that when used intransitively, the subject acts as the patient rather than the agent.
For example, consider these sentences concerning a kettle that boiled some water. In this situation, the kettle is the agent, while the water is the patient:
|Transitive, active voice||"The kettle boiled the water."||Subject = agent, object = patient|
|Passive voice||"The water was boiled (by the kettle)."||Subject = patient, (indirect object = agent)|
|Intransitive||"The water boiled."||Subject = patient|
Occasionally, two verbs together form an ergative verb, such as "rise"/"raise"; these are ergative verb pairs.