measured on an imaginary "keyboard of concepts". Of course, it doesn't
suffice to reach wide and plunk down any old way-you may hit a seventh
or a ninth! Perhaps the present analogy is like a ninth-chord-wide but
dissonant.
Picking up Patterns on All LevelsBongard problems were chosen as a focus in this Chapter because when
you study them, you realize that the elusive sense for patterns which we
humans inherit from our genes involves all the mechanisms of representa-
tion of knowledge, including nested contexts, conceptual skeletons and
conceptual mapping, slippability, descriptions and meta-descriptions and
their interactions, fission and fusion of symbols, multiple representations
(along different dimensions and different levels of abstraction), default
expectations, and more.
These days, it is a safe bet that if some program can pick up
patterns in one area, it will miss patterns in another area which, to us,
are equally obvious. You may remember that I mentioned this back in
Chapter I, saying that machines can be oblivious to repetition, whereas
people cannot. For instance, consider SHRDLU. If Eta Oin typed the
sentence "Pick up a big red block and put it down" over and over again,
SHRDLU would cheerfully react in the same way over and over again,
exactly as an adding machine will print out "4" over and over again,
if a human being has the patience to type "2+2" over and over again.
Humans aren't like that; if some pattern occurs over and over again,
they will pick it up. SHRDLU wasn't built with the potential for forming
new concepts or recognizing patterns: it had no sense of over and overview.
The Flexibility of LanguageSHRDLU's language-handling capability is immensely flexible-within
limits. SHRDLU can figure out sentences of great syntactical complexity, or
sentences with semantic ambiguities as long as they can be resolved by
inspecting the data base-but it cannot handle "hazy" language. For in-
stance, consider the sentence "How many blocks go on top of each other to
make a steeple?" We understand it immediately, yet it does not make sense
if interpreted literally. Nor is it that some idiomatic phrase has been used.
"To go on top of each other" is an imprecise phrase which nonetheless gets
the desired image across quite well to a human. Few people would be
misled into visualizing a paradoxical 50etup with two blocks each of which is
on top of the other--or blocks which are "going" somewhere or other.
The amazing thing about language is how imprecisely we use it and
still manage to get away with it. SHRDLU uses words in a "metallic" way,
while people use them in a "spongy'· or "rubbery" or even "Nutty-Putty-
ish" way. If words were nuts and bolts, people could make any bolt fit into
any nut: they'd just squish the one into the other, as in some surrealistic(^674) Artificial Intelligence: Prospects