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# Society of Mind

## 7.3 the puzzle principle

Many people reason that machines do only what they're programmed to do — and hence can never be creative or original. The trouble is that this argument presumes what it purports to show: that you can't program a machine to be creative! In fact, it is surprisingly easy to program a computer so that it will proceed to do more different things than any programmer could imagine in advance. This is possible because of what we'll call the puzzle principle.

Puzzle Principle: We can program a computer to solve any problem by trial and error, without knowing how to solve it in advance, provided only that we have a way to recognize when the problem is solved.

By trial and error we mean programming the machine systematically to generate all possible structures within some universe of possibilities. For example, suppose you wished to have a robot machine that could build a bridge across a stream. The most efficient program for this would simply execute a specific procedure, planned out in advance, to precisely place some boards and nails. Of course, you couldn't write such a program unless you already knew how to build a bridge. But consider the alternative below, which is sometimes called the generate and test method. It consists of writing a two-part program.

Generate. The first process simply produces, one after another, every possible arrangement of the boards and nails. At first, you might expect such a program to be hard to write. But it turns out to be surprisingly easy, once you appreciate that there is no requirement for each arrangement to make any sense whatsoever! Test. The second part of the process examines each arrangement to see whether the problem has been solved. If the goal were to build a dam, the test is simply whether it holds back the stream. If the goal were to build a bridge, the test is simply whether it spans the stream.

This possibility makes us reexamine all our old ideas about intelligence and creativity, since it means that, in principle, at least, we can make machines solve any problems whose solutions we can recognize. This is rarely practical, however. Consider that there must be a thousand ways to attach two boards, a million ways to connect three of them, and a billion ways to nail four boards together. It would take inconceivably long before the puzzle principle produced a workable bridge. But it does help, philosophically, to replace our feeling of mystery about creativity by more specific and concrete questions about the efficiency of processes. The main problem with our bridge-building machine is the lack of connection between its generator and its test. Without some notion of progress toward a goal, it is hard to do better than mindless chance.