Abstract
Regularity and irregularity are among the most widely invoked notions in linguistics. The terms are backed up by a long and venerable tradition, and yet (or maybe therefore) different disciplines and authors seem to be using them for very different phenomena and in very different ways. The most frequent usage conflates or replaces other notions such as type frequency, productivity, (non-)concatenative morphology, storage vs. computation, predictability etc. An assessment of these and other variables in Icelandic verbal inflection reveals that most of them are in practice strongly correlated. I conclude, however, that this is largely unsurprising by virtue of the definitional dependencies holding between those notions. It is empirically doubtful whether there exists a single underlying phenomenon or category which the terms designate. In addition, given their multiple and overlapping senses, and the existence of separate, unambiguous labels for the relevant underlying notions, I contend that the terms 'regular' and 'irregular' should be ideally abandoned in scientific literature in order to avoid ambiguity, sloppy reasoning and misunderstandings and to facilitate cross-linguistic comparison and interdisciplinary dialogue.