A possible constraint on non-affixal inflection

Starting out from observational gaps in the Norwegian verb inflection, a constraint is suggested on non-affixal inflection. A previous suggestion is shown not to suffice. A revised version, the Stem Alternation Constraint, is suggested. This constraint seems empirically adequate when confronted with examples from German, Italian and Polish. Theoretical implications are considered. The constraint indicates that paradigms are organised, that Bybeeʹs notion of autonomy is useful, and that non-affixal inflection is not a ragbag of isolated facts without theoretical interest.