Two-Fund Separation in Dynamic General Equilibrium

The purpose of this paper is to examine the two-fund separation paradigm in the context of an infinite-horizon general equilibrium model with dynamically complete markets and heterogeneous consumers with time and state separable utility functions. With the exception of the dynamic structure, we maintain the assumptions of the classical static models that exhibit two-fund separation with a riskless security. In addition to a security with state-independent payoffs agents can trade a collection of assets with dividends following a time-homogeneous Markov process. We make no further assumptions about the distribution of asset dividends, returns, or prices. Agents have equi-cautious HARA utility functions. If the riskless security in the economy is a consol then agents' portfolios exhibit two-fund separation. But if agents can trade only a one-period bond, this result no longer holds. Examples show this effect to be quantitatively significant. The underlying intuition is that general equilibrium restrictions lead to interest rate fluctuations that destroy the optimality of two-fund separation in economies with a one-period bond and result in different equilibrium portfolios.