There is little or no argument these days that Black English Vernacular (BEV) is a reality and that it is stigmatized. There is still a need, however, in spite of many studies of spoken varieties of BEV, for teachers to know what governs its occurrence in writing. This study concentrates on the written manifestation of BEV, on explaining which features occur, how often they occur, why they occur, whether the occurrence of some features implies the occurrence of others, and why some individuals are more likely to write in the Vernacular than others. Major findings include: a wide divergence in linguistic performance; a lack of correlation between the occurrence of BEV features with extra-linguistic factors, including socio-economic status, mobility, and racial isolation; a lack of correlation between occurrence of BEV features and scores on a standardized college entrance examination; the existence of an implicational relationship between several key features, the most significant of which is that deletion of the copula/auxiliary "be" implies the use of all other BEV features; and, most importantly, the significance of the degree and kind of motivation individuals have in determining their ability to write in Edited American English. (Author)