Sentence:  ...distinctions among states of affairs are reflected to a striking degree in distinctions among "Aktionsart" types. That is, situations are expressed by state verbs or predicates, events by achievement verbs or predicates, and actions by <WSD>activity</WSD> verbs or predicates. 
Meaning of the word marked with <WSD> tags:  The lexical aspect (aktionsart) of verbs or predicates that change over time and have no natural end point.