Habitual be, also called invariant be, is the use of an uninflected be in African-American English (AAE), Caribbean English and certain dialects of Hiberno-English to mark habitual or extended actions in place of the Standard English inflected forms of be, such as is and are. In AAE, use of be indicates that a subject repeatedly does an action or embodies a trait. In General American English, however, the use of (an inflection of) be means only that an individual has done an action in a particular tense, such as in the statement "She was singing" (the habitual is "She sings").
In South-West Hiberno-English, the habitual takes a different form, with do being added to the sentence as a supplement. Instead of saying "She is late" or "They are always doing that," "She do be late" and "They always be doing that" are used. It is descended from the Irish language, which uses the verb Bí, the habitual tense of the verb "to be".
It is a common misconception that AAE simply replaces is with be across all tenses, with no added meaning. In fact, AAE uses be to mark a habitual grammatical aspect, which is not explicitly distinguished in Standard English. For example, to be singing means to sing habitually, not to presently be singing. In one experiment, children were shown drawings of Elmo eating cookies while Cookie Monster looked on. Both Black and white subjects agreed that Elmo is eating cookies, but the Black children said that Cookie Monster be eating cookies.
Hypothesized sources
The source of habitual be in AAE is still disputed. Some linguists suggest it came from the finite be in the 17th-to-19th century English of British settlers (perhaps especially those from South West England, but the usage may be the recent "Mummerset" in this context). Other linguists believe that it came from Scots-Irish immigrants, whose Ulster Scots dialects mark habitual verb forms with be and do be.
One hypothesis is that habitual be simply diffused into New World Black English from Hiberno-English (HE) through contact in the Caribbean. Evidence includes the fact that both dialects structure sentences with the habitual be almost identically:
(1) Even when I do be round there with friends, I do be scared. (HE)
(2) Christmas Day, well, everybody be so choked up over gifts and everything, they don't be too hungry. (AAE)
Criticism of that hypothesis stems from the fact that there is no evidence that be has been used as a habitual marker either in the past or today in Caribbean creoles of English. Instead, Caribbean English uses the preverbal does to mark habitualness. They use be only as filler between does and the sentence's predicate.
The hypothesis states that the geographical differences in use of be and do (be), in Northern and Southern HE respectively, accounts for the difference in use of be and does (be) in AAE and Caribbean English respectively. In the 17th and the 18th centuries, Northern HE speakers immigrated more to North America, and Southern HE speakers immigrated to the Caribbean Islands, both working alongside blacks. Although the expansion to include the differences in the dialects of HE accounts for the absence of habitual be in Caribbean English creoles, the hypothesis has its disadvantages as well. The first problem is the distribution of do and be again. In Southern HE, do is more common with be than other verbs, but in Caribbean English, does is less common with be than other verbs. Hibernian English marks habitualness with be, and Caribbean English rarely marks it, if at all. A second problem is that there is not sufficient evidence to show that Southern HE speakers did not introduce do (be) to the American colonies since there were Southern HE speakers in the colonies who worked closely with Black people.