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Grammatical tense locates an event or state relative to a temporal reference point, commonly the time of speaking. A language may mark it through verb forms or grammatical constructions. Temporal reference itself is broader: a time expression can convey when something happens without being a tense marker.^[ref]

In the simple past statement “The train arrived”, the arrival precedes the speech time. Writing event time $E$ and speech time $S$, this simple relation is $E<S$. “The train was arriving” also has past tense, but changes grammatical aspect by presenting the arrival as unfolding. Thus the two categories answer different questions. A precise model states its reference point and interpretation; identifying a past-looking ending alone does not settle every temporal relation in a complex utterance.

SIL International is a language-focused organization whose name appears as the publisher of linguistic reference materials and software documentation. Its glossary distinguishes concepts such as grammatical tense, which locates a situation relative to a reference time, and grammatical aspect, which describes its temporal presentation.^[ref][ref]

Its language-technology work includes FieldWorks Language Explorer, software for organizing lexical entries, analyzing texts and describing grammar. An investigator can connect an observed word form with an analysis into morphemes, then compare that analysis across further recorded examples. Such tools make a proposed linguistic morphology inspectable; the stored analysis still needs evidence from language use.^[ref]