An anticausative verb is any intransitive verb which has an effect on its subject, without describing the cause of this effect. Only the patient of the verb, acting as the subject of the sentence, serves as an argument of an anticausative verb. Usually, other context from prior sentences can imply a cause or an agent for the verb, but within the strict syntax of the sentence containing the verb itself, no such indication is offered, and in the case of some specific verbs, it is impossible to give the agent within the same clause.
Anticausative verbs are a category of unaccusative verbs. While these terms usually describe the same verbs, some unaccusative verbs are more obviously anticausative, while others, such as "die" and "fall," are more ambiguous, and still others cannot be anticausative at all. Many English anticausatives also qualify as alternating ambitransitive verbs, able to alternate between transitive and intransitive states, by changing the position of the patient of the verb. Below are examples of such causative alteration.
John broke the lamp. → The lamp broke. (Passive voice: The lamp was broken.)
You sank my battleship! → My battleship sank. (Passive voice: My battleship was sunk.)
Note that passive voice operates separately from anticausation, using a different inflected form of the verb, assisted by a helping verb, demoting the agent of causation from the subject (the core argument of the verb) and even removing it from the clause entirely. The agent can be reintroduced to the sentence, usually through the use of "by," such as "The lamp was broken by John," and "The battleship was sunk by my opponent." Likewise, in active voice anticausative statements, the agent can be reintroduced through the use of "because of," such as "The lamp broke because of John," and "My battleship sank because of you." Verbs which can exist in passive voice in English are usually unable to be non-anticausative unaccusatives. "He died," for example, does not offer the option of passive voice, and it does not imply a specific agent without the addition of a "because" or "from" phrase. These same principles can also occur with middle voice and mediopassive voice in Romance languages and Slavic languages, among others, but English does not feature these grammatical voices at all.
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