Parts of our vocabulary for describing actions have wide commitments,
other parts do not. So you cannotminegold unless gold gets mined;
although you cantry tomine gold in a place where there is nothing but
fool’s gold, and you couldprospect forgold in a world in which there was
no such stuVat all. The vocabulary appropriate for classiWcation of
behaviour will depend upon whether our interest is focused on the agents
or on their environment, on psychological explanation and prediction, or
on the acquisition and communication of other facts (see section 5 below,
for the related distinction betweenexplanatoryandsemanticcontent).
4.3 Do mental states supervene on local facts?Let us try another tack. Consider the way in which physicalism about the
mental is often expressed: by claiming that mental states supervene upon
brain states. It is often said that there can be no diVerences at the level of
the mental, without some corresponding diVerences in the brain. If two
people have distinct mental states, then there must – it is alleged – be some
other(physical) diVerence between them (presumably in their brains)
which explains the diVerence. In contrast with mental/physical dualism, we
no longer accept that mental facts can ‘Xoat free’ of physical facts. On the
contrary, almost everyone today is a physicalist.
This now gives rise to an argument for narrow content. For brain states
are surelynotindividuated relationally. No one would want to maintain
that Petereand Petertware in two diVerent brain states, merely on the
grounds that the one has water in his environment whereas the other has
twater in his. Equally, no one would want to say that Mary and Joan must
be in distinct brain states, merely on the grounds that the tables con-
fronting them are numerically distinct. So, if brain states are non-relation-
ally (that is, narrowly) individuated, and mental states supervene on brain
states, then mental states must be narrowly individuated as well. For
otherwise there would be (relational) mental diVerences without any cor-
responding brain diVerence.
On reXection, however, this argument, too, just begs the question in
favour of narrow content. For if mental states ‘ain’t (entirely) in the head’,
as wide-content theorists maintain, then, plainly, mental states will not
supervene on brain states alone. Rather, they will supervene on brain
statestogether with relational facts. This can still be fully consistent with
physicalism, provided that those relational facts are themselves physical
ones (as, indeed, they are).
A more promising strategy for a narrow-content theorist is to appeal to
the thought thatmental states should supervene upon causal powers. For
from the standpoint of explanatory psychology, we are only going to be
148 Content for psychology