Zeno Vendler distinguished four aspectual classes of verbs:
- states, which are static and do not have an endpoint ("know," "love");
- activities, which are dynamic and do not have an endpoint ("run," "drive");
- accomplishments, which have an endpoint and are incremental or gradual ("paint a picture," "build a house"); and
- achievements, which have an endpoint and occur instantaneously ("recognize," "notice").
We are trying to develop a more detailed classification of processes in Basic Formal Ontology by analyzing these and other aspectual characteristics of verbs. The latter have been studied by linguists and philosophers of language from a linguistic perspective, thus with a focus on how matters are described. Our focus, in contrast, is on what is the case in reality when different verb aspects are used -- thus providing an ontological perspective.