A characteristic principle of much contemporary antirealism is this: truth supervenes on evidence, in the sense that there can be no difference in truth value (between two statements, theories, worldviews, etc.) unless there is also a difference in epistemic value. In the first part of this essay, I will demonstrate this principle at work in the writings of two leading antirealists, Hilary Putnam and Nelson Goodman. In the remainder of the essay, I will argue that the principle is self-refuting in much the same way as the logical positivists' criterion of meaningfulness is: it fails to satisfy the requirements it seeks to impose on other views. There are ways of construing the principle to save it from selfrefutation, but they all have the effect of undermining its intended applications.

The Principle Exposed

Though never explicitly formulated, the supervenience principle plays a critical role in the arguments of Putnam and Goodman. Both writers make much of the fact that there are theories or descriptions of the world that are logically incompatible if taken at face value but that, at the same time, are in some sense equivalent. The equivalence in question is clearly supposed to be some sort of epistemic equivalence. It is not, however, to be understood in narrow empiricist fashion; it involves not merely covering equally well any relevant empirical data, but also fulfilling to the same degree any further constraints that reason may impose.