Messick's (1989) theory of test validity is profoundly influential (Hubley and Zumbo, 1996; Angoff, 1988) in part because it brings together disparate contributions into a unified framework for building validity arguments. At the heart of Messick's theory lies a synthesis of realism and constructivism with respect to both scientific facts and measurement. Within this synthesis there remains a tension between the evidential basis and the consequential basis for test interpretation and use. This cannot be sidestepped simply by limiting the evidential basis to test interpretation and the consequential basis to test use: Interpretation and use are not so easily held separate. The roles of constructivism and context in Messick's theory underline the inherent link between facts and values, but the assumption that facts are objective and values are subjective goes unquestioned in Messick's theory. The inherent link between facts and values combines with this assumption to produce the unresolved tension in Messick's theory. This suggests that a unified theory of test validity requires a theory of value justification.