In this paper I argue that a subpattern of Irish plural allomorphy 
should be analyzed as output optimizing in character. Specifically, I 
claim that stress-sensitive alternations between the plural suffixes 
-(e)anna and -(e)acha are conditioned by constraints on metrical 
well-formedness. This analysis connects with independent facts about the 
the prosodic prominence of [ax] sequences in Irish phonology. I further 
argue that an explanatory analysis of these patterns must make use of 
the notion of surface optimization. Alternative frameworks that eschew 
surface-oriented optimization mechanisms fail to account for synchronic 
and diachronic properties of the Irish plural system.