An anticausative verb (abbreviated ) is an intransitive verb that shows an event affecting its subject, while giving no semantic or syntactic indication of the cause of the event. The single argument of the anticausative verb (its subject) is a patient, that is, what undergoes an action. One can assume that there is a cause or an agent of causation, but the syntactic structure of the anticausative makes it unnatural or impossible to refer to it directly. Examples of anticausative verbs are break, sink, move, etc. Anticausative verbs are a subset of unaccusative verbs. Although the terms are generally synonymous, some unaccusative verbs are more obviously anticausative, while others (fall, die, etc.) are not; it depends on whether causation is defined as having to do with an animate volitional agent (does "falling" mean "being accelerated down by gravity" or "being dropped/pushed down by someone"? Is "old age" a causation agent for "dying"?). A distinction must be made between anticausative and autocausative verbs. A verb is anticausative if the agent is unspecified but assumed to be external (or even if its existence is denied), and it is autocausative if the agent is the same as the patient. Many Indo-European languages lack separate morphological markings for these two classes, and the correct class needs to be derived from context: (Lithuanian) Vežimelis atsirišo nuo krūmo. Anticausative: "The cart got untied from the bush" Arklys atsirišo nuo krūmo. Autocausative: "The horse got [itself] untied from the bush" (Russian) Чашка упала со стола и разбилась. Chashka upala so stola i razbilas'. Anticausative: "The cup fell from the table and got broken" Водитель разбился на горной дороге. Voditel' razbilsya na gornoy doroge. Autocausative: "The driver crashed (lit. broke himself) on a mountain road" Examples English In English, many anticausatives are of the class of "alternating ambitransitive verbs", where the alternation between transitive and intransitive forms produces a change of the position of the patient role (the transitive form has a patientive direct object, and this becomes the patientive subject in the intransitive). This phenomenon is called causative alternation. For example: He broke the window. → The window broke. Some pirates sank the ship. → The ship sank. Passive voice is not an anticausative construction. In passive voice, the agent of causation is demoted from its position as a core argument (the subject), but it can optionally be re-introduced using an adjunct (in English, commonly, a by-phrase).