 The notion of aspect according to Comrie refers to “[the] different ways of viewing the internal temporal constituency of a situation” (1976: 3). It is customary to distinguish between lexical and grammatical aspect. The following are examples concerning lexical aspect. Since Vendler (1967) linguists distinguish at least four aspectual classes. These are states like know, activities like run, accomplishments like cross the street and achievements exemplified by a verb like recognize. Accomplishments describe the internal temporal constituency of a situation in a more detailed way than (say) activities. Crossing the street, for example, includes the starting of a crossing activity which goes on for some time and involves a result state that is characterized by being on the other side of the street. No such elaborate descriptions are necessary for activities or achievements. There are grammatical means of distinguishing between these aspectual classes. For example, states and achievements cannot occur with the progressive while activities and accomplishments can; more about this below in  Section 5.    These differences are customarily considered to be lexical differences and this area is therefore dubbed lexical aspect. 