The lexical aspect or aktionsart ( [ʔakˈtsi̯oːnsˌʔa:t], plural aktionsarten [ʔakˈtsi̯oːnsˌʔa:tn̩]) of a verb is a part of the way in which that verb is structured in relation to time. Any event, state, process, or action which a verb expresses—collectively, any eventuality—may also be said to have the same lexical aspect. Lexical aspect is distinguished from grammatical aspect: lexical aspect is an inherent property of a (semantic) eventuality, whereas grammatical aspect is a property of a (syntactic or morphological) realization. Lexical aspect is invariant, while grammatical aspect can be changed according to the whims of the speaker.
For example, eat an apple differs from sit in that there is a natural endpoint or conclusion to eating an apple. There is a time at which the eating is finished, completed, or all done. By contrast, sitting cannot merely stop: unless we add more details, it makes less sense to say that someone "finished" sitting than it does to say they "stopped" sitting. This is a distinction of lexical aspect between the two verbs. Verbs that have natural endpoints are called "telic" (from Ancient Greek telos, end); those without are called "atelic".
Categories
Zeno Vendler (1957) classified verbs into four categories: those that express "activity", "accomplishment", "achievement" and "state". Activities and accomplishments are distinguished from achievements and states in that the former allow the use of continuous and progressive aspects. Activities and accomplishments are distinguished from each other by boundedness: activities do not have a terminal point (a point before which the activity cannot be said to have taken place, and after which the activity cannot continue – for example "John drew a circle") whereas accomplishments do. Of achievements and states, achievements are instantaneous whereas states are durative. Achievements and accomplishments are distinguished from one another in that achievements take place immediately (such as in "recognize" or "find") whereas accomplishments approach an endpoint incrementally (as in "paint a picture" or "build a house").
In his discussion of lexical aspect, Bernard Comrie (1976) included the category semelfactive or punctual events such as "sneeze". His divisions of the categories are as follows: states, activities, and accomplishments are durative, while semelfactives and achievements are punctual. Of the durative verbs, states are unique as they involve no change, and activities are atelic (that is, have no "terminal point") whereas accomplishments are telic. Of the punctual verbs, semelfactives are atelic, and achievements are telic. The following table shows examples of lexical aspect in English that involve change (an example of a State is 'know').
Another categorization is the described by Moens and Steedman based on the idea of the event nucleus