<p>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.</p>