The animal spirits hypothesis and the Benhabib-Farmer condition for indeterminacy

This paper provides a self-contained review of the introduction of the animal spirits hypothesis into the infinite horizon optimal growth model. The analysis begins with an economic discussion of Pontryagin’s maximum principles. Thereafter, I develop a version of the increasing-returns Benhabib-Farmer model by showing the possible sub-optimality of the central planner solution and deriving the bifurcation condition for indeterminacy. Moreover, I give some insights on how to model intrinsic and extrinsic uncertainty. Finally, analysing the equilibrium condition of the labour market, I provide an intuitive rationale for the mechanism that in this model might lead prophecies to be self-fulfilling