In retrospective languages obligatory occurrence of past tense implies the same for future tense, the converse holding for prospective languages.
Standardized
In retrospective languages, IF there is past tense, THEN there will be future tense. In prospective languages, IF there is future tense, THEN there will be past tense.
If a present tense may ordinarily mark a Moment of speech (MOS) future or if the latter may be unmarked, the system is prospective.If a present tense may ordinarily mark a MOS past or if the latter may be unmarked, the system is retrospective.
If a present tense may ordinarily mark a Moment of speech (MOS) future or if the latter may be unmarked, the system is prospective.If a present tense may ordinarily mark a MOS past or if the latter may be unmarked, the system is retrospective.