Now what does a symbol do, when awakened? A low-level description
would say, "Many of its neurons fire." But this no longer interests us. The
high-level description should eliminate all reference to neurons, and con-
centrate exclusively on symbols. So a high-level description of what makes a
symbol active, as distinguished from dormant, would be, "It sends out
messages, or signals, whose purpose is to try to awaken, or trigger, other
symbols." Of course these messages would be carried as streams of nerve
impulses, by neurons-but to the extent that we can avoid such phraseol-
ogy, we should, for it represents a low-level way of looking at things, and we
hope that we can get along on purely a high level. In other words, we hope
that thought processes can be thought of as being sealed off from neural
events in the same way that the behavior of a clock is sealed off from the
laws of quantum mechanics, or the biology of cells is sealed off from the
laws of quarks.
But what is the advantage of this high-level picture? Why is it better to
say, "Symbols A and B triggered symbol C" than to say, "Neurons 183
through 612 excited neuron 75 and caused it to fire"? This question was
answered in the Ant Fugue: It is better because symbols symbolize things, and
neurons don't. Symbols are the hardware realizations of concepts. Whereas
a group of neurons triggering another neuron corresponds to no outer
event, the triggering of some symbol by other symbols bears a relation to
events in the real world--or in an imaginary world. Symbols are related to
each other by the messages which they can send back and forth, in such a
way that their triggering patterns are very much like the large-scale events
which do happen in our world, or could happen in a world similar to ours.
In essence, meaning arises here for the same reason as it did in the
pq-system-isomorphism; only here, the isomorphism is infinitely more
complex, subtle, delicate, versatile, and intensional.
Incidentally, the requirement that symbols should be able to pass
sophisticated messages to and fro is probably sufficient to exclude neurons
themselves from playing the role of symbols. Since a neuron has only a
single way of sending information out of itself, and has no way of selectively
directing a signal now in one direction, now in another, it simply does not
have the kind of selective triggering power which a symbol must have to act
like an object in the real world. In his book The Insect Societies, E. O. Wilson
makes a similar point about how messages propagate around inside ant
colonies:
[Mass communication] is defined as the transfer, among groups,
of information that a single individual could not pass to another.^3It is not such a bad image, the brain as an ant colony!
The next question-and an extremely important one it is, too-
concerns the nature and "size" of the concepts which are represented in the
brain by single symbols. About the nature of symbols there are questions
like this: Would there be a symbol for the general notion of waterfalls, or
would there be different symbols for various specific waterfalls? Or would
both of these alternatives be realized? About the "size" of symbols, there are
questions like this: Would there be a symbol for an entire story? Or for a(^350) Brains and Thoughts