Among the most striking morphosyntactic characteristics shared by the Celtic languages are their elaborate consonant mutation systems. It is clear from the most cursory inspection that in such systems, the range of possible syntactic relations between mutation triggers and their targets is subject to principled limits. In a recent paper, Zwicky (1984) has hypothesized that trigger-target relations are universally restricted by the constraint in (1): (1) The trigger determining a rule feature for a morphophonemic rule must be adjacent to the affected word and c-command it (Zwicky, 1984:389).