Smitherman, G. (1977). Talkin and testifyin: The language of Black America. Wayne State University Press.

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An excerpt:

The most distinctive differences in the structure of Black Dialect are patterns using be (sometimes written and pronounced as bees or be’s). These forms are mainly used to indicate a condition that occurs habitually. Be is omitted if the condition or event is not one that is repeated or recurring. For example, The coffee bees cold means Every day the coffee’s cold, which is different from The coffee cold which means Today the coffee’s cold. In other words if you the cook and The coffee cold, you might only just get talked about that day, but if The coffee bees cold, pretty soon you ain’t gon have no job! (Smitherman, 1977, p. 19)