Keelefilosoofia raamat
Kroon defends this primarily by extend-
ing the "naming after" objection.
Natural-kind terms and "Twin Earth"
Kripke (1972/1980) and Hilary Putnam (1975a) went on to extend both the
semantic theory of rigid designation and the CausalHistorical Theory of
referring from singular terms to some predicates or general terms, chiefly
naturalkind terms, common nouns of the sort that refer to natural substances
or organisms, like "gold," "water," "molybdenum," "tiger," and "aardvark."
Such expressions are not singular terms, since they do not purport to apply
to just one thing. But Kripke and Putnam argued that they are more like
names than they are like adjectives. Semantically they are rigid; each refers
Proper names: Direct Reference and the CausalHistorical Theory 59
to the same natural kind in every world in which that kind has membership.
And some version of the CausalHistorical Theory characterizes their refer-
ring use.