Claims about the productivity of a given affix are generally made without differentiating productivity according to type of discourse, although it is commonly assumed that certain kinds of derivational suffixes are more pertinent in certain kinds of texts than in others. Conversely, studies in register variation have paid very little attention to the role derivational morphology may play in register variation.

This paper explores the relation between register variation and derivational morphology through a quantitative investigation of the productivity of a number of English derivational suffixes across three types of discourse in the British National Corpus (written language, context-governed spoken language, and everyday conversations). Three main points emerge from the analysis. First, within a single register, different suffixes may differ enormously in their productivity, even if structurally they are constrained to a similar extent. Second, across the three registers under investigation a given suffix may display vast differences in productivity. Third, the register variation of suffixes is not uniform, i.e. there are suffixes that show differences in productivity across registers while other suffixes do not, or do so to a lesser extent. We offer some tentative explanations for these findings and discuss the implications for morphological theory.