Language Variation and Change, 9 (1997), 333-347. Printed in the U.S.A. © 1997 Cambridge University Press 0954-3945/97 $5.00 + .00 Violable is variable: Optimality theory and linguistic variation GREGORY R. GUY York University ABSTRACT Optimality theory (OT) (McCarthy & Prince, 1993; Prince & Smolensky, 1993) has been proposed as a constraint-based theory of phonology in which the phonological facts of each language are accounted for by a language-specific ordering of a uni- versal inventory of constraints. The constraints, expressing desirable (i.e., optimal) phonological states, evaluate possible candidate forms, selecting the optimal out- put. Any constraint may be violated by a surface form if it is overridden by a higher- ranked constraint; the ordinal sequence of constraints provides a weak quantification of constraint effects. Variability has been treated within OT by varying constraint orders. This model is analogous in several important respects to the variable rule model (VR) of Labov (1969) and Cedergren and Sankoff (1974). In VR, variable constraints express desirable phonological states which are variably realized on the surface, when not overridden by other constraints; constraints are probabilistically quantified. This article compares the OT and VR models, arguing that the VR model is superior on theoretical and empirical grounds: constraint effects in VR are stable, transparent, and learnable. Moreover, the probabilistic treatment of constraint ef- fects allows VR to model successfully cases in which multiple violations of a single constraint lead to a cumulative reduction in likelihood of a form; such cases cannot be efficiently treated in OT. PRINCIPLES AND CONSTRAINTS IN PHONOLOGICAL THEORY Theoretical work in phonology over the last decade or so has made the study of phonological constraints and principles one of its main points of focus. This in- terest reflects two general tendencies in recent linguistic theory. First, there is the need—ever since the establishment of the overly powerful generative model—to devise principled constraints on the theory; second, there is interest in the Chom- skyan research program of discovering universal features of the human language faculty and universal grammar (UG). In phonological theory, these themes can be seen to underlie many of the proposals that have been made of general, possibly universal, principles such as the Obligatory Contour Principle, the Elsewhere Condition, the Strict Cycle Condition, and others. Most of these were proposed as An earlier version of this article was presented at NWAVE-XXIII. The work reported here was sup- ported by grant number 410-92-1765 from the Social Sciences and Humanities Research Council of Canada. 333