The concept of intelligence.
Rosch's theory of concepts, applied to the concept of intelligence, suggests that one's intelligence is just the degree to which one resembles a prototypically intelligent person. Because no single characteristics defines the prototype, there can be no adequate process-based definition of intelligence. In principle, a combination of many empirically derived measures into a single index—as in a Binet test—would be appropriate. In practice, many of the relevant characteristics are simply impossible to measure.