ABSTRACT
The words "intelligence" and "intelligent" are widely used with a variety of meanings in ordinary discourse. In its broadest sense, intelligence means simply the existence of rational thought, as in "human beings are intelligent life-forms." Some psychologists have broadened the definition of intelligence considerably to include human abilities and talents that are not usually considered to be cognitive reasoning skills. The nature and malleability of intelligence are intrinsically related issues, because some theories of intelligence have very definite implications about whether it can be changed. A fundamental problem in the developmental study of intelligence is that, as previously noted, Intelligence Quotient (IQ) cannot be reliably measured before ages three or four. Theories that IQ is determined mostly by inherited genes imply that IQ cannot be changed for individual children. In contrast, theories that IQ is a product of the environment clearly leave room for changing it through manipulation of environmental factors.
