 The last mentioned research line in contemporary analytical process philosophy takes its departure from mid-20th century philosophical and linguistic research on discourse about occurrences. Zeno Vendler (1957) and Anthony Kenny (1963) argued that actions can be sorted into various types according to certain logical and linguistic features of verbs denoting these actions. The resulting classifications of “action types” are similar, but Vendler’s fourfold division operated with fewer criteria and thus proved more influential: whether a “verb” denotes a “state”, “activity”, “accomplishment”, or “achievement” depends on whether in present tense the progressive form needed, whether it can be combined with the verb “finish,” or whether it applies an any moment of a temporal interval at which it applies. Certain problems with Vendler’s and Kenny’s classifications were first noted by linguists Henk Verkuyl (1972) and Barry Taylor (1977). Most seminal, however, was Alexander Mourelatos’ (1978) observation that the distinctions that Vendler and Kenny tried to capture do not pertain to the lexical semantics of “action verbs” but to the semantics of entire sentences, and not of sentences about actions but about occurrences in general. This renders the classificatory task much more complex than Vendler and Kenny envisaged. Since then the linguistic discussion has produced (under the keywords “Aktionsart,” “verbal aspect,” and “aspectuality”) a plethora of theories about the many different ways in which natural languages express the dynamic aspects of a situation. These linguistic theories provide essential data for analytical process ontology, but one must not overlook that there are language-specific interplays between verb semantics, tense system, and aspectual meanings, and that ontology should be guided by inferential differences that hold across  languages.[7]