Case Study: Planning Courses of Action - Thinking as Computation - page 179

9 Case Study: Planning Courses of Action

Intelligent behavior is made intelligent by the application of knowledge. We are able
to act intelligently because we know a lot about the world around us and are able
to bring this knowledge to bear on our decisions about what to do. In particular,
we make decisions not just by reacting to what we see, hear, or smell around us but
by deliberating about what we want and how to achieve it. For example, instead of
heading toward a file cabinet that contains something we want, we might first think
about it and decide to move in a completely opposite direction (if we need to get
the key that will unlock it). As another example, consider the deliberations involved
in a (traditional) wedding: the invitations, the ceremony, the dinner, the reception.
Hundreds, even thousands of decisions are pondered well in advance of the wedding
day itself. Nobody would call this sort of thinking intellectual, like playing chess or
discussing Schopenhauer, but it is clearly intelligent behavior of the highest order.
So what is the thinking that underlies these sorts of deliberations? In its simplest
formitis planning , contemplating various possible courses of actions, until we find
one that we believe will achieve what we want. This is the sort of thinking that is
investigated in this chapter.
To plan, we need to be able to think about the actions we can take, and imagine
what the world would be like if we took them. Unlocking a file cabinet will allow a
drawer to be opened if the right key is available. Contacting a property manager will
allow a wedding planner to discover if a hall can be rented for a reception. Planning
is not just thinking about the way the world is but about the way it can be . This
requires thinking about the state of the world and how that state is affected by what
we (and others) do. It is a major intellectual achievement of humans (and no doubt
other animals, too) to be able to step back from the world in this manner and imagine
it as being quite different from the way it is.

This chapter has four sections. Section 1 discusses two simple but very different
planning problems and how the planning process is really the same for both of them.
Section 2 considers a general planning program in Prolog, and applies it to three
planning problems. The final two sections consider how planning changes as the