Which theory of intelligence was proposed by Spearman?

Concept: Theories of intelligence explain the structure or determinants of mental ability in different ways. Psychometric (factor-analytic) theories statistically analyse correlations among test scores to identify how many ability 'factors' exist and how they relate — a single general factor, several independent group factors, or many specific factors. Process-oriented theories, by contrast, explain intelligence through the cognitive processes involved in solving a problem, rather than through a factor structure derived from test correlations.

Application: Charles Spearman (1904) analysed correlations among different mental-ability tests and concluded that performance on every task depends on two components: a single general factor 'g', common to all intellectual activity, plus a task-specific factor 's', unique to each particular test. He named this the Two-Factor Theory of Intelligence.

The other listed theories belong to different psychologists and structures:

• Group factor theory (Thurstone) — several independent 'primary mental abilities' (verbal, numerical, spatial, etc.) instead of one general factor.

• Multi-factor theory (Thorndike) — intelligence as a large aggregate of many specific, independent abilities, with no dominant general factor.

• Process-oriented theories (e.g. information-processing / cognitive-development approaches) — describe intelligence through the mental processes used while solving a problem, not through a fixed factor structure.

Since the question asks specifically for the theory Spearman himself proposed, the Two-Factor Theory of Intelligence is the answer.