Gödel, Escher, Bach An Eternal Golden Braid by Douglas R. Hofstadter

One of the basic viewpoints underlying the model is that all language use can

be thought of as a way of activating procedures within the hearer. We can

think of any utterance as a program-one that indirectly causes a set of

operations to be carried out within the hearer's cognitive system. This "pro-

gram writing" is .indirect in the sense that we are dealing with an intelligent

interpreter, who may take a set of actions which are quite different from those

the speaker intended. The exact form is determined by his knowledge of the

world, his expectations about the person talking to him, etc. In this program

we have a simple version of this process of interpretation as it takes place in

the robot. Each sentence interpreted by the robot is converted to a set of

instructions in PLANNER. The program that is created is then executed to

achieve the desired effect.I6

PLANNER Facilitates Problem Reduction

The language PLANNER, referred to here, is an AI language whose
principal feature is that some of the operations necessary for problem
reduction are built in-namely, the recursive process of creating a tree of
subgoals, subsubgoals, etc. What this means is that such processes, instead
of having to be spelled out time and time again by the programmer, are
automatically implied by so-called GOAL-statements. Someone who reads a
PLANNER program will see no explicit reference to such operations; in
jargon, they are user-transparent. If one path· in the tree fails to achieve the
desired goal, then the PLANNER program will "backtrack" and try
another route. "Backtracking" is the magic word as far as PLANNER is
concerned.
Winograd's program made excellent use of these features of
PLANNER-more exactly, of MICROPLANNER, a partial implementa-
tion of the plans for PLANNER. In the past few years, however, people
with the goal of developing AI have concluded that automatic backtrack-
ing, as in PLANNER, has definite disadvantages, and that it will probably
not lead to their goal; therefore they have backed off from it, preferring to
try other routes to AI.
Let us listen to further comments from Winograd on SHRDLU:

The definition of every word is a program which is called at an appropriate

point in the analysis, and which can do arbitrary computations involving the

sentence and the present physical situation.I7

Among the examples which Winograd cites is the following:

The different possibilities for the meaning of "the" are procedures which

check various facts about the context, then prescribe actions such as "Look for

a unique object in the data base which fits this description", or "Assert that the

object being described is unique as far as the speaker is concerned." The

program incorporates a variety of heuristics for deciding what part of the

context is relevant.I8

It is amazing how deep this problem with the word "the" is. It is probably

safe to say that writing a program which can fully handle the top five words

Artificial Intelligence: Retrospects 629