Jacob McDowell

Amid all his famously changeable views, Hilary Putnam held a long-standing commitment to semantic externalism about natural kind terms. Early on, Putnam claimed an affinity between this view and Saul Kripke’s work on natural kind terms as ‘rigid designators’. This led to many authors referring to the ‘Kripke-Putnam’ view of natural kind terms. Subsequently though, Putnam sought to distance his view from that of Kripke, particularly with regard to Kripke’s commitment to metaphysical necessity and essentialism – a commitment I regard as untenable in the face of actual scientific classification. I want to argue that rejecting these commitments of Kripke’s should have also forced Putnam to revise some of his most strongly held views. First, I will argue that externalism without essentialism cannot support Putnam’s own intuition about his Twin Earth thought experiment. Second, I will argue that Putnam loses a sufficiently general and univocal notion of ‘substance identity’ that was necessary for supporting his reading of the Twin Earth case and also for guaranteeing the reference of scientific terms across theory changes.

It is typically held that Thomas Kuhn was committed to a descriptivist view of the meaning of theoretical terms, and that his most infamous thesis – incommensurability – was a consequence of this. The causal theory of reference supposedly rules out incommensurability by allowing the extension of a term, rather than merely the intension, to (at least partly) constitute the meaning of the term, thereby ensuring that part of the ‘meaning’ remains constant across theory changes. It is therefore surprising to find Kuhn endorsing aspects of the causal theory in several later essays while still maintaining the possibility of incommensurability. This paper will investigate how Kuhn understood both the causal theory and incommensurability, such that his endorsement of both was not the bald-faced contradiction it would be according to the standard reading. In fact, many of the affinities of Kuhn’s view with the causal theory are part of what make incommensurability possible, or so I will argue. More generally, I will suggest that Kuhn should be thought of as rejecting the very idea that the meaning of scientific terms is some aggregate of extension and intension, or sense.