Focusing on the process of grammaticization, whereby
items with lexical meaning evolve into grammatical markers,
this article examines the future temporal reference sectors
of three diaspora varieties of African American English
which have evolved in linguistic isolates and compares
them with those of British-origin rural and mainstream
varieties of English. With one exception, the same constraint
hierarchies condition the selection of going to
across the board, indicating that their future temporal
reference systems are descended from a common source. All
other distinctions among the varieties result from their
differential positioning on the cline of ongoing grammaticization
of going to as a future marker. Operationalization
of constraints representing different stages of the development
of going to and comparison of their probability
values across communities confirm that the enclave and
the rural varieties retain conservative traits, visible
here in the form of variable conditioning, in contrast
to mainstream English, which is innovating. We suggest
that the major determinant of variability in the expression
of the future is the fact that the speech of isolated speakers,
whether of African or British origin, instantiates constraints
that were operative at an earlier stage of the English
language and that are now receding from mainstream varieties.