have been able to agree. This relation, calledsupervenience, is that any difference
in conscious events requires some corresponding difference in underlying neu-
ral activity. In other words, mental events supervene on neural events because
no two possible situations can be identical with respect to their neural proper-
ties while differing in their mental properties. It is a surprisingly wea krelation,
but it is better than nothing.
Supervenience does not imply that all differences in underlying neural activ-
ity result in differences in consciousness. Many neural events are entirely out-
side awareness, including those that control basic bodily functions such as
maintaining gravitational balance and regulating heartbeat. But supervenience
claims that no changes in consciousness can take place without some change
in neural activity. The real trick, of course, is saying precisely what kinds of
changes in neural events produce what kinds of changes in awareness.
1.1.2 The Problem of Other Minds
The functionalist arguments about multiple realizability are merely thought
experiments because neither aliens nor electronic brains are currently at hand.
Even so, the question of whether or not someone or something is conscious is
central to the enterprise of cognitive science because the validity of such argu-
ments rests on the answer. Formulating adequate criteria for consciousness is
one of the thorniest problems in all of science. How could one possibly decide?
Asking how to discriminate conscious from nonconscious beings brings us
face to face with another classic topic in the philosophy of mind: theproblem
of other minds. The issue at stake is how I know whether another creature (or
machine) has conscious experiences. Notice that I did not say ‘‘howweknow
whether another creature has conscious experiences,’’ because, strictly speak-
ing, I do not know whetheryoudo or not. This is because one of the most pe-
culiar and unique features of my consciousness is its internal, private nature:
Only I have direct access to my conscious experiences, and I have direct access
only to my own. As a result, my beliefs that other people also have conscious
experiences—and your belief that I do—appear to be inferences. Similarly, I
may believe that dogs and cats, or even frogs and worms, are conscious. But in
every case, the epistemological basis of my belief about the consciousness of
other creatures is fundamentally different from knowledge of my own con-
sciousness: I have direct access to my own experience and nobody else’s.
Criteria for Consciousness If our beliefs that other people—and perhaps many
animalsaswell—haveexperienceslikeoursareinferences,onwhatmightsuch
inferences be based? There seem to be at least two criteria.
1.Behavioral similarity. Other people act in ways that are roughly similar
to my own actions when I am having conscious experiences. When I ex-
perience pain on stubbing my toe, for example, I may wince, say ‘‘Ouch!’’
and hold my toe while hopping on my other foot. When other people do
similar things under similar circumstances, I presume they are experienc-
ing a feeling closely akin to my own pain. Dogs also behave in seemingly
analogous ways in what appear to be analogous situations in which they
might experience pain, and so I also attribute this mental state of being in
pain to them. The case is less compelling for creatures like frogs andVisual Awareness 11