This chapter examines intelligence and mental abilities, which are cognitive abilities that promote learning and adaptive behavior. The complex processes underlying mental abilities cannot be studied directly; instead, they must be inferred from a person’s actions in situations requiring their use. Intelligence tests are designed to measure a person’s general mental abilities.

Recent research indicates that experts do not yet agree on a single definition of "intelligence." Moreover, "intelligence" apparently means somewhat different things to experts and to nonexperts. In the early 1980s, Sternberg and his associates discovered that both experts and nonexperts described an intelligent person as someone with practical problem-solving ability and verbal ability. But laypersons included social competence in their concepts of intelligence, whereas experts put more emphasis on motivation.