Externalism and a Posteriori Semantics

It is widely held that the meaning of certain types of terms, such as natural kind terms, is individuated externalistically, in terms of the individual's external environment. Recently a more radical thesis has emerged, a thesis we dub 'a posteriori semantics.' The suggestion is that not only does a term's meaning depend on the external environment, but so does its semantics. One motivation for this is the aim to account for cases where a putative natural kind term fails to pick out a natural kind: The term may have a standard externalist semantics (if it picks out a natural kind) or a more descriptivist one (if it does not). Knowing which semantics applies will therefore require detailed empirical knowledge. This move has also been employed in cases where a singular term, such as a name, fails to have a reference. We argue that a posteriori semantics is inherently implausible, since the type of semantics common terms should be given ought not to be conditional on details of chemistry or physics. A number of difficulties for the position—'metaphysical,' epistemological, and methodological—are articulated. Finally, we suggest that a posteriori semantics misconstrues the way in which semantics is empirical.