Rationality Of Beliefs And Model Consistency

The assumption of rational expectations (RE) plays two roles in economic models: it imposes restrictions on behaviour of agents, and it ensures model consistency. Dissatisfaction with RE on behavioural grounds has, in a variety of models, led to its replacement by more behaviourally plausible postulates. However, replacing RE by ad hoc behavioural postulates may result in internally inconsistent models. This work introduces a conceptual framework within which the nature of the issue can be described, and points to potential problems that the abandonment of RE entails. We argue that the RE-based notion of consistency is model-specific rather than general, and introduce a weaker consistency condition that is relevant for non-RE models. To assess the consistency of these models, we propose a test and illustrate its use taking an example from the recent literature. Broader implications of the findings are discussed.