Swampman, response-dependence, and meaning

Toward the end of their chapter “Externalism and the Impossibility of Massive Error,” Lepore and Ludwig (2007a, pp. 335–42) explain—correctly, I think—that the privileged position that Davidson grants the radical interpreter in being able to determine all things semantic suggests that his externalism is synchronic and physical. They clarify: “Synchronic externalism holds that our thought contents depend only on our current environment and our dispositions to respond. . . . Physical externalism holds that our thought contents are determined in part by our relations to our physical, nonsocial environment” (p. 336). They might have added that Davidson’s externalism concerns thought and talk. But their point is clear enough. Lepore and Ludwig then observe that Davidson’s externalism is in fact physical and diachronic. “He holds . . . that there is a historical element to thought content” (p. 337). They contend that Davidson’s argument for diachronism is his Swampman thought experiment: