The cognitive theory that currently exerts the greatest influence on social psychologists is attribution theory, the formalized version of which was introduced by Harold Kelley in 1967. The theory poses a view of man as lay scientist, attempting to infer causes for the effects he observes. The causes he attributes determine his view of his social world, and this view may determine his behavior. An extremely broad range of phenomena, from Asch's conformity research to Schachter's emotion work, may be usefully described as instances of the causal attribution process at work. In fact, it seems quite possible that Kelley's most important contribution may ultimately be seen to have been his creation of a language, or roadmap, with which to describe and interrelate diverse social psychological phenomena.

In addition to his organizational contribution, Kelley posited three formal sources of influence on the causal attribution process. In attempting to attribute causes for events of the form “Actor responds in X fashion to situation A,” the lay attributor responds to three sources of information: distinctiveness information (Does the actor respond in X fashion in all situations of the general type, or only in situation A?); consistency information (Does the actor respond in X fashion at all times, under a broad variety of circumstances, or does he respond in X fashion only occasionally?); and consensus information (Do most other actors respond in X fashion, or is the response relatively rare?).