Wallage (2008) argues for a model of the Middle English Jespersen Cycle in which each of its diachronic stages are functionally equivalent competitors in the sense proposed by Kroch (1989). However, recent work on the Jespersen Cycle in various Romance languages by Schwenter (2006), Hansen (2009) and Hansen & Visconti 2009) has argued that the forms in competition during the Jespersen Cycle are not simply diachronic stages, but perform different pragmatic or discourse functions. Hansen (2009) and Hansen & Visconti (2009) suggest that functional change may therefore underpin the Jespersen Cycle in these languages. Hence this paper explores the interface between pragmatic or functional change, and change in the syntax of sentential negation.Analysis of data from the PPPCME2 (Kroch & Taylor 2000) show that ne (stage one) and ne...not (stage two) are similarly functionally differentiated during the ME Jespersen Cycle: ne...not is favoured in propositions that are discourse-old (given, or recoverable from the preceding discourse), whereas ne is favoured in propositions that are discourse-new. Frequency data appear to show the loss of these constraints over time. However, I argue that these frequency data are not conclusive evidence for a shift in the functions of ne or ne...not. Indeed, the results of a regression analysis indicate that these discourse constraints remain constant throughout Middle English, in spite of the overall spread of ne...not as the Jespersen Cycle progresses. Therefore, I conclude the spread of ne...not is independent of these particular discourse constraints on its use, rather than the result of changes in, or loss of, these constraints.