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In a lecture on philosophy of science, the lecturer said something to the effect that the necessity of identity and Kripke's theory of rigid designators "provides a path back to scientific realism" in contrast to the anti-realism of positivists and the relativism of Kuhn. The typical "both the morning star and the evening star are venus" and "water == H2O" examples were given to illustrate the necessity of identity, and then the discussion moved straight to explaining what scientific realism was, without really explaining why realism and Kripke's result are connected.

So how does one make the leap from Kripke's ideas to scientific realism?

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It does make sense in a way. Kripke's thesis is that proper names have essences, properties that belong to them of necessity, not accidentally. Putnam extended this thesis to "natural kinds" of objects, whose essential properties "carve nature at the joints", in Plato's metaphor, rather than according to our cultural biases, practical needs, etc., those would be the "artificial kinds".

This provides a semantic framework for a realist ontology, as opposed to semantic theories of Quine and Wittgenstein that reduce meaning to use in a language game, which requires no realist referents, or deny such referents to "natural kinds", which only acquire meaning as placeholders in a theoretical "web of belief". E.g. gold, water, etc., only mean in the context of chemistry, which relates to experience only as a whole, and reflects pragmatic human considerations as much as nature. Of course, if "natural kinds" do "carve nature at the joints" then there is something "in nature" corresponding to them, even if we do not yet discern it fully and precisely. This provides a framework where Kripke-Putnam reference is preserved across scientific revolutions despite Kuhn's "incommensurable paradigms", this promise of continuity is what attracted Putnam in 1970s, when he was still a realist, and others. Rigid designation is tangential to this, it enters only in that if we believe in nature given "essential properties" then it makes sense to keep them fixed across possible worlds when analyzing "physical" counterfactuals. Norris's Realism, Reference, & Possible Worlds makes the case for essentialism as an aid to realism along the lines of Putnam of 1970s and the OP quoted lecture.

However, Kripke's essentialism is not "a path back to scientific realism", that would be putting the cart before the horse. It works if we presuppose a form of scientific realism, that would be scientific essentialism, but in itself it is a semantic theory that purports to describe use of language based on speakers' "linguistic intuitions" (similarly rigid designation purports to account for "modal intuitions"), not metaphysics. Ironically, Kripke himself is partial to Wittgenstein, and Putnam apparently discarded even his very weak "internal realism", which was of Quinean pseudo-variety.

That folk intuitions are faithful to "reality" is also highly doubtful, or as Cummins put it "there is no more reason to think that innate philosophy is a good basis for philosophy than that innate physics is a good basis for physics". Cummins's Reflections on Relective Equilibrium is a sharp critique of Kripke-Putnam's approach in general:"It is commonplace for researchers in the Theory of Content to proceed as if the relevant intuitions were undisputed. Nor is the reason for this practice far to seek. The Putnamian take on these cases is widely enough shared to allow for a range of thriving intramural sports among believers. Those who do not share the intuition are simply not invited to the games". Recently even semantic adequacy of Kripke-Putnam's theory of natural kinds has come under fire, see Ben-Yami's Natural Kind Terms.

  • Putnam was a realist then he wasn't, believed in Quantum Logic then he didn't, believed in CTM and Functionalism, then he didn't,...it's getting hard to follow the guy. – Alexander S King Apr 15 '16 at 16:42
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    @Alexander Putnam is an extreme case but it is not unheard of. Kant was a champion of Leibnizian metaphysics for decades before he took it apart in CPR, Nietzsche was a Kantain on mind and knowledge and a libertarian on free will before he started mocking noumena and became a compatibilist. Popper announced his conversion the other way in a public lecture, like Putnam, same one as his change of mind on evolution. People intimately familiar with a doctrine are best placed to see its flaws, and there is something to be said for intellectual honesty, philosophy can use more Putnams if you ask me. – Conifold Apr 17 '16 at 1:39

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