From coordination devices to coordination failures: on the changing epistemology of sunspots since the 1970s

Abstract

The widespread adoption of the rational expectations hypothesis in macroeconomic literature from the 1970s onwards has often overlooked the issue of coordinating individual decisions, particularly regarding expectations. How is common knowledge, essential for rational expectations equilibrium, established? When common knowledge supports multiple equilibria, how do expectations converge to a specific one? These pivotal questions have always been at the core of sunspot literature, which emerged at the turn of the 1980s, albeit sometimes implicitly. While unspots were initially regarded by pioneers David Cass and Karl Shell as essential coordination devices, their epistemological status evolved with the introduction of competing models in ndogenous fluctuations (chaos, bifurcations, deterministic cycles) and the transition from the overlapping generations to the infinitely lived agent framework. Ultimately identified as anticipation shocks, sunspots were portrayed as instability triggers and markers of coordination failures. However, recent advancements in sunspot theory, especially in the areas of financial crises and experimental economics, have started to rehabilitate the original interpretation of sunspots as coordination mechanisms. This article maps out the historical development, shedding light on the evolving concepts surrounding sunspots.