This thesis is concerned with the nature of syntactic defaults and what their investigation can tell us about the theory of grammar. Since Chomsky (1995) first introduced feature-checking, we’ve understood the need to value features to be central to how the grammar regulates grammaticality. The failure of an uninterpretable feature to receive a value and be deleted before reaching the interface induces the derivation crash that differentiates grammatical sentences from ungrammatical ones. Defaults offer us an interesting domain of inquiry because we would expect them to be impossible to generate in this type of system; nonetheless, they surface in a number of core syntactic domains. The existence of syntactic defaults raises three central questions: first, how is it that defaults are produced in a system where the failure to value features causes ungrammaticality? Second, how is it that the production of defaults is constrained such that whatever mechanism accounts for their production doesn’t overapply to instances where they aren’t licit? Finally, given that syntactic defaults appear to involve underspecification, what can an understanding of the default mechanism tell us about the role of underspecification in the syntactic domain?In this thesis, I focus our attention on two arenas: defaults in the domains of case and phi- agreement. A number of proposals have been made in recent years that address these issues, at least in part. They share a similar logic: the way to account for how defaults surface in the system is to abandon the notion that failing to value a feature is fatal to the derivation. I will argue in this thesis that by making small modifications to the generally accepted framework, we can account for the production of defaults without having to abandon that notion.One such departure is dependent case theory – a configurational approach to case whereby case features are valued not through their relationships with case-assigning functional heads, but rather by their relative positions to other nominals. Built into this system is a default case, assigned as a last resort to nominals that have failed to receive a more specific value. While a desire to understand defaults is not what originally guided the proposal of dependent case theory, its ability to easily account for their production has certainly contributed to its widespread adoption. In the domain of phi-agreement, another departure called obligatory operations addresses the default issue more directly and proposes a new understanding of what drives derivations. It is not the need to value features that explains why phi-agreement is obligatory, but rather that the operations responsible for establishing those dependencies are obligatory themselves. By shifting the explanatory burden to the triggering of operations, rather than their outcomes, obligatory operations claims that syntactic operations can fail, without inducing ungrammaticality; thus providing a solution to the default production problem. While the departures in both arenas have directly addressed the issue of how defaults are produced, neither has been too successful in understanding how that production is constrained. Furthermore, in order to solve the production issue each has to abandon the central tenet of feature valuation.I argue that in light of a host of deep conceptual and empirical issues regarding these two departures, we are better served to handle the default problem by making modest modifications to the standard syntactic framework that the field has adopted since (Chomsky, 2000, 2001). I extend a decomposition of Agree that is sensitive to inherent hierarchical relationships between features to both produce and – more importantly – constrain the distribution of syntactic defaults (Béjar, 2003). This decomposition produces three outcomes of agreement – rather than the standard two – and it is in this third outcome where we find syntactic defaults and other interesting types of underspecification and repairs. What is available to us through this proposal is an understanding of how defaults are both produced and how that production is constrained and the simultaneous ability to maintain standard assumptions about the role of feature valuation in regulating grammaticality. Through this system, we can also gain further insight into the nature of underspecification and its role in the syntactic component.
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