B.A. Uspenskij's theory that there was Church Slavonic-Russian diglossia in medieval Rus' has provoked a great deal of controversy in the last few years, stimulated in particular by the publication of his Istorija russkogo literaturnogo jazyka (XI-XVII w.) in 1987. 1 The diglossie approach, which has won its share of supporters as well as detractors, differs from previous, genetically oriented treatments of the early Russian linguistic situation in that it attempts to reconstruct the normative thought of medieval bookmen. By stressing the role of linguistic consciousness, the proponents of diglossia make explicit and important claims about the pragmatic aspects of language use in medieval Rus' in particular, about how writers perceived and utilized linguistic variation. In this article, I will be concerned chiefly with these pragmatic ramifications of Uspenskij's approach. I will begin by discussing the main points of the diglossie theory and will then examine certain aspects of it that seem to be in conflict with the observable characteristics of early Russian written sources.