 Grammatical aspect

Grammatical aspect presents a temporal view of an event or state, for example as ongoing or as a whole. It concerns how the event is viewed, whereas grammatical tense concerns its relation to a temporal reference point. Affixes and auxiliary constructions can express aspectual distinctions.^[ref]

Compare “The train arrived” with “The train was arriving”. Both locate the situation in the past, but the second presents an unfolding situation and does not by itself assert a completed arrival. Comparing “is arriving” with “was arriving” instead changes tense while retaining the progressive construction. Such contrasts help isolate which part of an interpretation comes from each grammatical choice. A formal semantics can encode those differences explicitly, rather than treating every temporal expression as the same kind of label.