8 - Feature-value Logics: Some Limits on the Role of Defaults

Abstract

This chapter discusses feature-value logics. It present a valuable assessment of the use of defaults in linguistics and discusses the issue of whether it is possible in particular to make sense of defaults in constraint-based linguistic theories that are supposed to have a declarative interpretation. Defaults should be limited to a single role; ruling out specifically the essential use of defaults in characterizing the combinatoric relation between basic and nonbasic elements. It is tempting to appeal to a default statement d in case it is impossible or inconvenient to characterise the sets of situations in which d does or does not hold. Moreover, it is meaningless to invoke defaults as linguistic statements. Under the nonmonotonic constraint-based view of defaults, applying some default d to some representation x amounts to determining the maximal subpart of d which is consistent with x, call this d’ and conjoining x and d’. If defaults are indeed ordered in regard to the rest of the theory, then it is easier to characterise in as general a way as possible how that ordering comes about, that is, what theoretical and empirical motivation there is for the postulation of domains which limit the potential failure of a default. Furthermore, considerable work would be needed to demonstrate that the use of defaults does not endanger an interpretation of the grammar. A computational criticism of defaults hinges on the claim that a simple construal of defaults does not result in effective constraints on the search space generated by a grammar. A stronger construal of defaults than as a simple ranking of nondeterministic choices is required in cases where a set of defaults and a representation to another representation which is maximally specific in regard to the defaults is needed.