The topic time of the verb of the sentence may coincide with the time of speech (present tense) or precede it (past tense). The languages of the world form two large groups with respect to whether or not they have such a grammatical distinction.[1] Where such a distinction does exist, the past tense is prototypically the marked form.

The perfect (single occurrence, specific, completed actions) generally refers to the past, and so many languages use the perfect, in addition to the present and the imperfect past[2], to express completed past actions. Some languages mark remoteness distinctions within the perfect. Such distinctions include “today’s past” and “yesterday’s past” or earlier, and some languages can even distinguish two recent pasts and three distant pasts. These may include the very distant past or a mythological past.

To determine the parameter value for a language, the past tense should be considered only as it appears in independent main clauses.

Types:

NoPst:  There is no grammatical distinction between past and non-past.

1Pst:  There is one grammatically distinct past tense.

2Pst:  There are two grammatically distinct past tenses: a general past (imperfect) and the perfect.

XRemPst:  There are x grammatically distinct past tenses that express the distance of the event in time. (X should be replaced with the actual number of past tenses.)[3]

[1] A grammatical distinction is only thought to exist when the past tense is expressed on the verb itself, rather than through the use of a separate adverbial in the sentence.

[2] A contrast in which one form expresses the general unfinished past and another expresses the progressive is not considered to be an example of separate tenses; progressiveness is an aspect, not tense.

[3] The general past tense should not be included in this number.