In this talk I examine the semantic underpinnings of argument realization,
using argument/oblique alternations as a case study, where a single
participant can be realized either as a direct argument or an oblique with
respect to a particular verb (e.g. English "John loaded the wagon with
hay/John loaded hay onto the wagon").  Drawing on data from a variety of
languages, I argue that such alternations are universally governed by the
relative informativity of different realization options:  direct argument
realizations are associated with more entailments about their role in the
event than their alternant oblique realizations, where the exact contrasts
are verb specific but cluster into broader semantic categories.  Much
recent work in predicate decompositions fails to provide a uniform
characterization of this general contrast.  I argue that it is instead
best characterized in a theory of argument realization that takes
verb-specific "lexical entailments" as its basis.  To this end I sketch a
framework for analyzing argument/oblique alternations in terms of Dowty
(1989, 1991), where thematic roles are defined as sets of entailments and
the relative informativity of alternating realizations in terms of subset
relationships between thematic roles.  This works serves to (a) provide a
general characterization for argument/oblique alternations, (b) update the
proto-role approach of Dowty (1991) to include a theory of oblique
realization and (c) support a general theory of argument realization based
directly on verb-specific semantic contrasts.