In the multilingual history of England, the period following the Norman Conquest in 1066 is a particularly intriguing phase, but its code-switching patterns have so far received little attention. The present article describes and analyses the multilingual practices evinced in London, British Library, MS Stowe 34, containing one instructional prose text from c. 1200, "Vices and Virtues". This religious treatise contains numerous instances of code-switching into Latin and also reiteration of the Latin content in English. Reiteration of this type is referred to as "support" here, which not only captures the reiterative character of the English wording accompanying the Latin, but also explicates its main function: to facilitate understanding of the incorporated Latin terms and quotations which appear throughout the text with the global function of authorising the teaching imparted by the author. While both the Latin switches and their support derive from sources familiar to the author, the exact origin of the supporting expressions is difficult to pin down, although parallels exist in older literature. Together, code-switching and support deliver both a sense of authority and direct access to religious teaching.