In this lecture, Thomson explores what intelligence is. He discusses the tendency to see intelligence and instinct as separate entities, and why he thinks this is inaccurate; the idea that thinking is simply trial and error using concepts and imagery rather than action; and the correlation between consciousness and intelligence in relation to the flashes of insight that come from the unconscious.

He also discusses the work of Spearman, suggesting that Spearman's two factor theory does not adequately represent the complexity of intelligence.