has a well-defined position, occupies a particular volume, has a definite shape,
and has a specific mass. Conscious experiences, such as perceptions, remem-
brances, beliefs, hopes, and desires, do not appear to have readily identifiable
positions, volumes, shapes, and masses. In the case of vision, however, one
might object that visual experiencesdohave physical locations and extensions.
There is an important sense in which my perception of a red ball on the table is
located on the table where the ball is and is extended over the spherical volume
occupied by the ball. What could be more obvious? But a substance dualist
would counter that these are properties of the physical object that I perceive
rather than properties of my perceptual experience itself. The experience is in
my mind rather than out there in the physical environment, and the location,
extension, and mass of these mental entities are difficult to define—unless one
makes the problematic move of simply identifying them with the location, ex-
tension, and mass of my brain. Substance dualists reject this possibility, believ-
ing instead that mental states, such as perceptions, beliefs, and desires, are
simply undefined with respect to position, extension, and mass. In this case,
it makes sense to distinguish mental substances from physical ones on the
grounds that they have fundamentally different properties.
We can also loo kat the issue of fundamental properties the other way
around: Do experiences have any properties that ordinary physical matter does
not? Two possibilities merit consideration. One is that experiences aresubjective
phenomenain the sense that they cannot be observed by anyone but the person
having them. Ordinary matter and events, in contrast, areobjective phenomena
because they can be observed by anyone, at least in principle. The other is that
experiences have what philosophers callintentionality: They inherently refer to
things other than themselves.^1 Your experience of a boo kin front of you right
now is about the boo kin the external world even though it arises from activity
in your brain. Thisdirectednessof visual experiences is the source of the confu-
sion we mentioned in the previous paragraph about whether your perceptions
have location, extension, and so forth. The physical objects to which such per-
ceptual experiences refer have these physical properties, but the experiences
themselves do not. Intentionality does not seem to be a property that is shared
by ordinary matter, and if this is true, it provides further evidence that con-
scious experience is fundamentally different.
It is possible to maintain a dualistic position and yet deny the existence of
any separate mental substances, however. One can instead postulate that the
brain has certain unique properties that constitute its mental phenomena. These
properties are just the sorts of experiences we have as we go about our every-
day lives, including perceptions, pains, desires, and thoughts. This philosophi-
cal position on the mind-body problems is calledproperty dualism.Itisaform
of dualism because these properties are taken to be nonphysical in the sense of
not being reducible to any standard physical properties. It is as though the
physical brain contains some strange nonphysical features or dimensions that
are qualitatively distinct from all physical features or dimensions.
These mental features or dimensions are usually claimed to beemergent prop-
erties: attributes that simply do not arise in ordinary matter unless it reaches a
certain level or type of complexity. This complexity is certainly achieved in the
human brain and may also be achieved in the brains of certain other animals.
4 Stephen E. Palmer