The Effects of Prosodic Constraints on Reduplication in Luiseño Plural Nouns Traditional studies of Luiseño plural noun morphology (e.g. Kroeber and Grace 1960, Munro and Benson 1973, Elliot 1991) assume an Item-and-Arrangement prefixing analysis of reduplication in which length alternations between long and short vowels in the same morpheme are explained by successive application of ordered rules. This accurately explains the data, but at the expense of stipulation of the phenomena rather than by reference to externally motivated constraints on licit syllable structure and morphological features. Traditional analyses, importantly, also do not explain exactly why a prefixing analysis as (4) below might suggest.           (1) 'ta:nat  'blanket'        'ta:tanat  'blankets'           (2) 'tukmal  'basket'       'tu:tukmal 'baskets'           (3) Su'Na:l  'woman'      SuSNalum   'women'           (4) a'hi:cum 'orphan'      ahi:hicum  'orphans' (Where <S> is a voiceless retroflex fricative, <N> a velar nasal, and <c> a voiceless postalveolar affricate.) In this paper, I attempt to show how vowel chain shift phenomena in Luiseño could be handled within a constraint-based theory of phonology like OT, by the interaction of prosodic alignment constraints with differentiated mora faithfulness constraints.  However, the invocation of templatic constraints necessary here such as those used by Kager (1999) for another Uto-Aztecan language, Southeastern Tepehuan, suggests that if templatic constraints are indeed a salient feature of the speakers' internal grammar, they are stipulations not of the reduplicant itself, but the conditions under which the reduplicant surfaces.  All this opens the question of exactly how phonologists should treat reduplicants and whether they should best be seen as a primarily phonological or a morphological phenomenon.       Elliot, Eric. 1991. Papers from the American Indian Languages Conferences. Carbondale, Illinois.         Southern Illinois University. Kager, René.  1999. Optimality Theory.  Cambridge, Cambridge University Press. Kroeber, A. L. and George William Grace. 1960.  The Sparkman Grammar of Luiseño.           Berkeley and Los Angeles, University of California Press. Munro, Pamela and P. Benson. 1973  "Reduplication and Rule Ordering in Luiseño".  IJAL 39, 15-21.