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DAVID BARNETTIS WATER NECESSARILY IDENTICAL TO H2O?(Received in revised form 26 June 1998)The scientific essentialist doctrine asserts that the following are
examples of a posteriori necessary identities: water is H2O; gold
is the element with atomic number 79; and heat is the motion of
molecules. Evidence in support of this assertion, however, is difficult
to find. Both Hilary Putnam and Saul Kripke have argued convincingly for the existence of a posteriori necessities. Furthermore,
Kripke has argued for the existence of a posteriori necessary identities in regard to a particular class of statements involving proper
names. Neither Kripke nor Putnam, however, has argued convincingly that sentences containing syntactically complex terms or
descriptive phrases can express a posteriori necessary identities. I
will argue by way of a hypothetical example that water is H2O
does not express a necessary identity. My argument is unique in
that it attacks the relevant sufficiency claim needed to underwrite
this putative necessary identity.1 That is, even if we grant that water
is necessarily composed of H2O, we should not accept that H2O
necessarily forms water.I shall not challenge the claim that there are a posteriori
necessary identities involving syntactically complex expressions or
descriptive phrases. (There are rigid descriptions and, hence, true
necessary identities expressed with them. First, utterly trivial ones
such as the first natural number = the first natural number. Second,
slightly less trivial ones such as Hesperus = the thing with which
Hesperus is identical. Third, nontrivial a priori ones such as 12 =
the sum of 5 and 7. And, fourth, nontrivial a posteriori ones such as
the thing with which Hesperus is identical = the thing with which
Phosphorus is identical.) Rather, I wish to stimulate investigation
into the scope of the relevant scientific-essentialist claims. My
argument that water is H2O does not express a necessary identity
should call into question, for instance, whether heat is necessarilyPhilosophical Studies 98: 99112, 2000.
2000 Kluwer Academic Publishers. Printed in the Netherlands.100 DAVID BARNETTidentical to the motion of molecules and whether gold is necessarily
identical to the element with atomic number 79.Dont eat the water! shouts your friend, with a grin, as you walk
down the gate to your ship. You are taking off on a space-ship for
twin earth,...