this article, we will show that one Muskogean gradation process, the so-called y-grade of Choctaw, calls upon prosodic circumscription as well. The Choctaw y-grade displays a complex system of interdependence between base and derivative, while at the same time requiring a cross-categorial invariant like the Arabic iambic template. Our investigations of Choctaw have been guided almost entirely by Nicklas's (1974, 1975) penetrating studies of this language. Nicklas provides a clear and evidently exact description of the complex phonology and morphology of this language. We have also consulted Ulrich's (1986) more recent treatment of a somewhat different dialect. Our primary focus, however, has been on the body of internally consistent material presented by Nicklas. In the remainder of this article, we proceed as follows. Section 2 provides a brief overview of the essentials of prosodic circumscription theory. Section 3 discusses the prosodic phonology of Choctaw, taking in turn syllable structure, foot structure, and minimal-word effects. Section 4 introduces the y-grade formation. Subsequent sections turn to details of the analysis, seeking additional confirmation or clarification where -2appropriate. Section 5 discusses the relation between two distinct uses of the iamb in the y-grade, as prosodically circumscribed base and as target for template-mapping. Section 6 discusses the process of medial gemination in the y-grade, arguing that it is formally independent of template-mapping. Section 7 takes up the phenomenon of final syllable extraprosodicity, finding that it has a pervasive role in this language. Some speculations on truncating morphology are also included. The article concludes with a summary of the formal basis of y-grade formation. 2. Outline of Prosodic Cir...

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