Sociolinguistic variation in the copula system of Black English was studied in the light of the linguistic history of the dialect and universal constraints on possible grammars. An attempt was made to identify sociological factors which account for the fact that the grammar of American Black English does not exhibit evidence for a creole stage in its development while Jamaican and other creoles do exhibit such evidence. The structural implications of variation in the realization of one form of the copula in Black English--"is"--were considered for phonetically full, contracted, or zero forms. (Author)