force look-ahead, hoping to crush all types of opposition. But it has not
worked. Perhaps someday, a look-ahead program with enough brute force
will indeed overcome the best human players-but that will be a small
intellectual gain, compared to the revelation that intelligence depends
crucially on the ability to create high-level descriptions of complex arrays,
such as chess boards, television screens, printed pages, or paintings.Similar LevelsUsually, we are not required to hold more than one level of understanding
of a situation in our minds at once. Moreover, the different descriptions of
a single system are usually so conceptually distant from each other that, as
was mentioned earlier, there is no problem in maintaining them both; they
are just maintained in separate mental compartments. What is confusing,
though, is when a single system admits of two or more descriptions on
different levels which nevertheless resemble each other in some way. Then
we find it hard to avoid mixing levels when we think about the system, and
can easily get totally lost.
Undoubtedly this happens when we think about our own
psychology-for instance, when we try to understand people's motivations
for various actions. There are many levels in the human mental
structure-certainly it is a system which we do not understand very well yet.
But there are hundreds of rival theories which tell why people act the way
they do, each theory based on some underlying assumptions about how far
down in this set of levels various kinds of psychological "forces" are found.
Since at this time we use pretty much the same kind of language for all
mental levels, this makes for much level-mixing and most certainly for
hundreds of wrong theories. For instance, we talk of "drives"-for sex, for
power, for fame, for love, etc., etc.-without knowing where these drives
come from in the human mental structure. Without belaboring the point, I
simply wish to say that our confusion about who we are is certainly related
to the fact that we consist of a large set of levels, and we use overlapping
language to describe ourselves on all of those levels.Computer SystemsThere is another place where many levels of description coexist for a single
system, and where all the levels are conceptually quite close to one another.
I am referring to computer systems. When a computer program is run-
ning, it can be viewed on a number of levels. On each level, the description
is given in the language of computer science, which makes all the descrip-
tions similar in some ways to each other-yet there are extremely important
differences between the views one gets on the different levels. At the lowest
level, the description can be so complicated that it is like the dot-description
of a television picture. For some purposes, however, this is by far the most
important view. At the highest level, the description is greatly chunked, and
Levels of Description, and Computer Systems 287