action verb a verb applied to an agent and describing an activity, an action, or an attempt at or a culmination of an action. Verbs applying to agents may be distinguished in two basic ways: by whether they can take the progressive (continuous) form and by whether or not there is a specific moment of occurrence/completion of the action named by the verb. An activity verb is one describing something that goes on for a time but with no inherent endpoint, such as ‘drive’, ‘laugh’, or ‘meditate’. One can stop doing such a thing but one cannot complete doing it. Indeed, one can be said to have done it as soon as one has begun doing it. An accomplishment verb is one describing something that goes on for a time toward an inherent endpoint, such as ‘paint’ (a fence), ‘solve’ (a problem), or ‘climb’ (a mountain). Such a thing takes a certain time to do, and one cannot be said to have done it until it has been completed. An achievement verb is one describing either the culmination of an activity, such as ‘finish’ (a job) or ‘reach’ (a goal); the effecting of a change, such as ‘fire’ (an employee) or ‘drop’ (an egg); or undergoing a change, such as ‘hear’ (an explosion) or ‘forget’ (a name). An achievement does not go on for a period of time but may be the culmination of something that does. Ryle singled out achievement verbs and state verbs (see below) partly in order to disabuse philosophers of the idea that what psychological verbs name must invariably be inner acts or activities modeled on bodily actions or activities. A task verb is an activity verb that implies attempting to do something named by an achievement verb. For example, to seek is to attempt to find, to sniff is to attempt to smell, and to treat is to attempt to cure. A state verb is a verb (not an action verb) describing a condition, disposition, or habit rather than something that goes on or takes place. Examples include ‘own’, ‘weigh’, ‘want’, ‘hate’, ‘frequent’, and ‘teetotal’. These differences were articulated by Zeno Vendler in Linguistics and Philosophy (1967). Taking them into account, linguists have classified verbs (and verb phrases) into four main aspectual classes, which they distinguish in respect to the availability and interpretation of the simple present tense, of the perfect tenses, of the progressive construction, and of various temporal adverbials, such as adverbs like ‘yesterday’, ‘finally’, and ‘often’, and prepositional phrases like ‘for a long time’ and ‘in a while’. Many verbs belong to more than one category by virtue of having several related uses. For example, ‘run’ is both an activity and an accomplishment verb, and ‘weigh’ is both a state and an accomplishment verb. Linguists single out a class of causative verbs, such as ‘force’, ‘inspire’, and ‘persuade’, some of which are achievement and some accomplishment verbs. Such causative verbs as ‘break’, ‘burn’, and ‘improve’ have a correlative intransitive use, so that, e.g., to break something is to cause it to break. See also PHILOSOPHY OF LANGUAGE , SPEECH ACT THEOR. K.B.