Lexical aspect

The lexical aspect or Aktionsart (, plural "Aktionsarten" ) of a verb is part of the way in which that verb is structured in relation to time. Any event, state, process, or action that a verb expresses (collectively, any "eventuality") may also be said to have the same lexical aspect. Lexical aspect is distinguished from grammatical aspect by being an inherent (semantic) property of an eventuality. Grammatical aspect is a (syntactic or morphological) property of a realization. Lexical aspect is invariant, but 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 can merely stop. Unless more details are added, it makes less sense to say that someone "finished" sitting than it does to say someone "stopped" sitting. That is a distinction of these verbs' lexical aspect. Verbs that have natural endpoints are called
"telic" (from Ancient Greek "telos", end), and those without natural endpoints are called "atelic".
Theories of aspectual class.
Although all theories of lexical aspect recognize that verbs divide into different classes, the details of the classification differ. An early attempt is that of Vendler (1957), which recognizes four classes ("activity", "accomplishment", "achievement" or "state"). There have been numerous modifications of Vendler's system, notably Comrie's (1976) introduction of a "durative" versus "punctual" contrast, as well as Moens & Steedman's (1988) notion of an "event nucleus".
Vendler's (1957) classification.
Zeno Vendler (1957) classified verbs into four categories on whether they express "activity", "accomplishment", "achievement" or "state". Activities and accomplishments are distinguished from achievements and states in that the first two 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 has taken place and after which cannot continue: "John drew a circle"), but accomplishments have one. Of achievements and states, achievements are instantaneous, but states are durative. Achievements and accomplishments are distinguished from one another in that achievements take place immediately (such as in "recognise" or "find"), but accomplishments approach an endpoint incrementally (as in "paint a picture" or "build a house").
Comrie's (1976) classification.
In his discussion of lexical aspect, Bernard Comrie (1976) included the category semelfactive or punctual events such as "sneeze". His divisions of the categories were as follows: states, activities, and accomplishments are durative, but 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').
Moens and Steedman's (1988) classification.
Another classification is proposed by Moens and Steedman, based on the idea of the event nucleus
Syntactic analyses of event structure.
Aspectual classes can be analyzed as differing in their event structure, and this has led to the development of syntactic analyses of event structure, with each aspectual class treated as having a distinct syntactic structure.