Many philosophers believe that absolute necessity is “logical” or “conceptual” in such a
way as to be confined to a mental or abstract realm and that it cannot escape from this
playground of the logicians to determine the real world in any wayIf, on the other hand, it
is a necessary truth that God exists, this must be a necessary truth that explains a real
existence (God's); indeed it provides the ultimate explanation of all real existenceThus, if
God's existence
end p.438
follows from his essence in such a way as to be necessary, his essence is no mere
logicians' plaything but a supremely powerful cause. (1987, 213–14)
Like Swinburne, I regard Platonism (or modal realism) as unsatisfactory. The main
reason is that it leaves us in the dark about the nature of necessity; we simply have no
idea, on this account, what makes a proposition necessary or why a proposition's
necessity should have the importance it apparently does have. That an essence should be
a “supremely powerful cause” is no doubt an exciting idea, but this combination of
excitement and obscurity is a dubious recommendation for a philosophical theory. The
obscurity lends itself to an unbridled faith in “modal intuition,” and to an excessive
reliance on thought experiments that is inherently anti-empirical. The obscurity is not
relieved if possible worlds are taken as primitive; doing this simply refuses to address the
question as to what makes possible worlds possible.
On the other hand, Swinburne's nominalism does not seem to be a satisfactory alternative.
When he says that the laws of logic “are simply generalizations about language” (1994,
108), he arguably leaves himself unable to account for the necessity that is characteristic
of logical truth. As a third option, I propose modal conceptualism, a view that, like
nominalism, denies that logical necessity and possibility pertain to the mind-independent
world, but that does not, like nominalism, make them merely properties of linguistic
expressions. Instead, necessity and possibility pertain to concepts, understood as ways it
is possible for a mind to grasp and classify the world and its contents. Conceived thus as
possibilia, concepts are necessary entities, existing even in worlds where there are no
minds to think them. Logical impossibility is then a matter of contradiction in concepts
and propositions, and from impossibility possibility and necessity can be defined in the
usual way. A possible world is one that is free from contradiction; a necessary truth is
one whose denial is explicitly or implicitly self-contradictory.
The most formidable challenge to this conceptualist account is found in the “synthetic
necessary truths” championed by Saul Kripke. Kripke (1980) convinced many
philosophers that “Hesperus = Phosphorus” and “Water is H 2 O” are necessary truths, in
spite of the fact that the negations of these propositions do not appear to be contradictory.
The right way of dealing with these examples is the one proposed by Alan Sidelle.
According to Sidelle (1989, 34), the key to such situations lies in “analytic general
principles of individuation” of the form
(x)(If x belongs to kind K, then if p is x's P-property, then it is necessary that x is p).
The particular principle that applies to chemical kinds such as water is
(x)(If x is a chemical kind, then if p is x's chemical formula, then it is necessary that x is
p).
end p.439