Have you ever watched a crab on the shore crawling backward in search of the Atlantic Ocean, and missing? That’s the way the mind of man operates.

– H. L. Mencken (1880–1956)

The previous chapter discussed how an agent perceives and acts, but not how its goals affect its actions. An agent could be programmed to act in the world to achieve a fixed goal or set of goals, but then it would not adapt to changing goals, and so would not be intelligent. An intelligent agent needs to reason about its abilities and goals to determine what to do. This chapter abstracts the problem of an agent deciding how to achieve a goal as the problem of searching for a path in a graph.