On December 13, 1994, a group of fifty-two experts in the scientific study of intelligence and allied fields provided the following unified definition of intelligence in the Wall Street Journal:
Intelligence is a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings—“catching on,” “making sense” of things, or “figuring out” what to do.
This is a reasonable definition of intelligence. It includes a description of behaviors relating to attention, perception, and learning that we would certainly want to include as key aspects of intellectual functioning. What’s more, this definition captures how most people—especially in Western cultures conceptualize a “smart” person. When we talk about someone being “smarter” than someone else, we tend to invoke the notion of quick reasoning and problem solving. This conceptualization pervades Western media, such as Jeopardy and The Big Bang Theory.
Another claim of the Wall Street Journal definition, however, is that intelligence, as measured by IQ tests, is a “very general mental capability.” There is one sense in which this statement is surely correct, but a few other senses in which we reach very thorny territory.
It is empirically true that the cognitive abilities that are measured on IQ tests are positively correlated with each other, giving rise to a “general intelligence factor”.* It is also true that the cognitive skills that are most strongly related to IQ (e.g., abstract reasoning, working memory, vocabulary, visual-spatial mental rotation) are highly general in the sense that they facilitate the speed and efficiency of learning novel and complex information across a wide range of contexts. It’s difficult to imagine a situation in which one is conscious and processing information that doesn’t draw whatsoever on these cognitive skills.
However, since IQ test scores are just that-- test scores. The scores themselves don’t actually have any causal properties. To say that IQ itself is a very general capacity reifies the IQ test. It is becoming increasingly clear in the field of intelligence that IQ is best thought of as an emergent property (not cause) of a range of cognitive mechanisms that are positively related to each other, and influence each other during the course of development.* In other words, IQ is a summary score, not the driver itself of cognitive potential.