It is relatively rare for a language to totally lack any grammatical means for marking the future. Most languages have at least one or more weakly grammaticalized devices for doing so. In this chapter, we have therefore decided to map only the inflectionally marked future tenses, inflectional marking being a relatively clear criterion (although there are some borderline cases where it is unclear if one is dealing with a clitic or an affix). Inflectional markings more often tend to be obligatory and also on the whole have a wider range of uses. For instance, they regularly show up in temporal and subordinate clauses, where periphrastic future-marking devices are relatively rare. They also appear systematically (often obligatorily) in sentences which express clear predictions about the future (which are independent of human intentions and planning), whereas less grammaticalized constructions often tend to be predominantly used in talk of plans and intentions—a fact which is explainable from the diachronic sources of future tenses, which have been fairly well studied (Bybee et al. 1994: 243-280). In most cases, inflectional future tenses derive from periphrastic constructions (employing auxiliaries or particles), which are in turn derived from constructions expressing such notions as obligation (‘must’), volition/intention (‘want’), and motion (‘go’ and ‘come’). However, a future tense may develop out of an earlier non-past or imperfective as an indirect effect, for example of the functional expansion of an earlier progressive—the future uses are what is left of the old category after that expansion.
The modal overtones that tend to go with futures have led many linguists to question their status as tenses (e.g. Lyons 1968: 306-311). In the approach presented in our general introduction, it is generally not expected that one will be able to make an unequivocal classification of the elements of tense-aspect-mood systems into neat compartments. From a diachronic point of view, it may be noted that one result of the progressive grammaticalization of futures is that the temporal component of their semantics becomes more dominant relative to the modal component.
Many grammars subsume grammatical future-marking devices under the heading "irreal(is)", especially when their range of use includes negated sentences, counterfactual conditionals, imperatives, etc. With Bybee et al. (1994: 240), we take the view that the distribution of irrealis categories varies too much across languages for them to be acknowledged as a viable cross-linguistic type; such categories are here counted as inflectional futures, if they are expressed inflectionally and cover the same range of uses as other future tenses.
