Case Study: Playing Strategic Games - Thinking as Computation - page 209

10 Case Study: Playing Strategic Games

One of the main complications that can arise in planning is that other agents may be
performing actions at the same time as you are, which can interfere with what you
are doing. In a sense, this is what is involved in playing a game like chess. The object
of the game is simple enough, to capture the other player's king. But a plan to achieve
that goal cannot be a sequence of moves like the plans in chapter 9. Instead, each time
you make a move, your opponent gets a turn to play and will make a move to try to
stop you from attaining your goal. You must then decide what to do next, and the
process iterates. Ideally, you will figure out a strategy that will eventually lead to your
goal no matter what your opponent does along the way. The thinking that is required
to do this is the subject matter of this chapter.
Why should we care about games like this? The answer is that playing a strategic
game like chess is considered to be a major intellectual challenge. We are awed by the
prodigies who can play well at an early age, and we see chess champions as demon-
strating remarkable prowess—not physical but mental prowess: clear, unadulterated
thinking at its very finest.
Of course, this chapter is not about chess itself but about playing games in general.
The ideas explored here apply to a wide variety of games, although not to every-
thing that is called a game. The focus in this chapter is on games with the following
characteristics:

Discrete-move and turn-taking. This excludes games where the players are
continuously moving at the same time,

such as physical games, and many

first-person video games.

Deterministic. This excludes games where chance is involved, such as Monopoly
or backgammon.
Two-person. This excludes solitaire and multiplayer games like Clue.

Perfect-information. This excludes games where part of the state of the game is
hidden from the other player, as in Scrabble or Battleship.