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Hilary Putnam has famously argued that we can know that we are not brains in a vat because the hypothesis that we are is self-refuting.1 While Putnam’s argument has generated interest primarily as a novel response to skepticism, his original use of the brain in a vat scenario was meant to illustrate a point about the “mind/world relationship.”2 In particular, he intended it to be part of an argument against the coherence of metaphysical realism, and thus to be part of a defense of his conception of truth as idealized rational acceptability. Putnam’s argument has drawn a good deal of criticism already, but it will be argued here that these criticisms fail to capture the central problem with Putnam’s argument. Putnam’s conclusions about the self refuting character of the brain in a vat hypothesis, rather than simply being a consequence of his semantic externalism, will be shown to be actually out of line with central and plausible aspects of his own account of the relationship between our minds and the world. Reflections on intentionality and semantics ultimately give us no compelling reason to suppose that the beliefs expressed by claims like “I am a brain in a vat” could not be true,3 but (pace Putnam) this supports neither skepticism nor metaphysical realism.

One of the most influential contemporary philosophers, Hilary Putnam's involvement in philosophy spans philosophy of mind, philosophy of language, ontology and epistemology and logic. This edited volume explores Putnam's contribution to the contemporary realist and pragmatist debate and includes Putnam's comments on each issue raised.

The paper I gave at the Dublin conference celebrating Hilary Putnam’s 80th birthday was “Resurrecting Biological Essentialism” (2008). This was suitable for a celebratory event because it defended Putnam’s position on biological essentialism (1975) from the consensus in the philosophy of biology. This consensus has led to some severe criticisms of Putnam. Michael Ruse, for example, places Putnam, along with Saul Kripke and David Wiggins, “somewhere to the right of Aristotle” on essentialism and talks of them showing “an almost proud ignorance of the organic world” (1987, 358n). John Dupré argues that the views of Putnam and Kripke are fatally divergent from “some actual biological facts and theories” (1981, 66). I argue that the consensus is quite wrong about essentialism and hence that these criticisms are misplaced.

In the following discussion, I examine what constitutes the dialectical strain in Putnam’s thought. As part of this examination, I consider Putnam’s (1981) criticism of the fact/value dichotomy. I compare this criticism to Putnam’s analysis of the metaphysical realist’s position, a position which has occupied Putnam’s thinking more than any other philosophical stance. I describe how Putnam pursues a chargeof self-refutation against the metaphysical realist and against the proponent of a fact/value dichotomy, a charge which assumes dialectical significance. So it is that the self-refuting nature of these positions is linked to their unintelligibility. My conclusion relates Putnam’s dialectical project to his wider philosophical ambitions, ambitions which are influenced in large part by Wittgensteinian considerations.

Two of Hilary Putnam's model-theoretic arguments against metaphysical realism are examined in detail. One of them is developed as an extension of a model-theoretic argument against mathematical realism based on considerations concerning the so-called Skolem-Paradox in set theory. This argument against mathematical realism is also treated explicitly. The article concentrates on the fine structure of the arguments because most commentators have concentrated on the major premisses of Putnam's argument and especially on his treatment of metaphysical realism. It is shown that the validity of Putnam's arguments is doubtful and that realists are by no means forced to accept the theses Putnam ascribes to them. It is concluded that Putnam fails to give convincing arguments for rejecting mathematical or metaphysical realism. Furthermore, Putnam's internal realism is discussed critically.

Hilary Putnam and Nelson Goodman are two of the twentieth century's most persuasive critics of metaphysical realism, however they disagree about the consequences of rejecting metaphysical realism. Goodman defended a view he called irrealism in which minds literally make worlds, and Putnam has sought to find a middle path between metaphysical realism and irrealism. I argue that Putnam's middle path turns out to be very elusive and defend a dichotomy between metaphysical realism and irrealism.