This paper derives the explicit solution of a dynamic stochastic optimal consumption problem for infinitely-lived agents whose preferences exhibit, in the presence of non-diversifiable labour income uncertainty, a constant elasticity of intertemporal substitution and constant absolute risk aversion. The constancy of the elasticity of intertemporal substitution, which implies that marginal utility at zero consumption is infinite, guarantees that the non-negativity constraint on consumption is never binding along the optimal path. The assumption of constant absolute risk aversion allows an explicit computation of human wealth, and provides a simple representation of the precautionary savings motive.

This paper introduces, within the context of an infinite horizon optimal consumption problem, a parametric class of Kreps-Porteus nonexpected utility preferences—generalized isoelastic utility—which distinguishes attitudes toward risk from behavior toward intertemporal substitution. Some of the theoretical and empirical implications for macroeconomics of these state- and time-nonseparable preferences are examined.

We demonstrate that stochastic bubbles which have a constant, exogenous, probability of collapsing may exist, in general equilibrium, on an intrinsically useless and unbacked asset (money). This may happen provided that the probability q that the bubble will persist next period is large enough and exceeds a threshold level Q which we call the minimum rate of confidence. This condition is always violated when the economy without bubble is dynamically efficient. It is more likely to be satisfied, in dynamically inefficient economies, the larger the “size” of the inefficiency (as measured by the excess of the growth rate over the no-bubble interest rate). We study both exchange and production economies.

It is often argued that a rational bubble, because it is positive, must increase the price of a stock. This argument is not valid in general: as soon as bubbles affect interest rates, the fundamental value of a stock depends on whether or not a bubble is present. The existence of a rational bubble then might, by raising equilibrium interest rates, depress the fundamental to such an extent that the sum of the positive bubble and decreased fundamental falls short of the fundamental, no-bubble price. Under conditions made precise below, there can therefore be price decreasing bubbles, and an asset can be undervalued.

Arguing that total consumer wealth is unobservable, we invert the (approximate) consumption function to reconstruct, in a world with Kreps-Porteus generalized isoelastic preferences, (i) the wealth that supports the agents' observed consumption as an optimal outcome and (ii) the rate of return on the consumers' wealth portfolio. This allows us to (approximately) price assets solely as a function of their payoffs and of consumption—in both homoskedastic or heteroskedastic environments. We compare implied equilibrium returns on the wealth portfolio to observed stock market returns and gauge whether the stock market is a good proxy for unobserved aggregate wealth.

Credit market imperfections influence the labor market and aggregate economic activity. In turn, macroeconomic factors have an impact on the credit sector. To assess these effects in a tractable general-equilibrium framework, we introduce endogenous search frictions, in the spirit of Peter Diamond (1990), in both credit and labor markets. We demonstrate that credit frictions amplify macroeconomic volatility through a financial accelerator. The magnitude of this general-equilibrium accelerator is proportional to the credit gap, defined as the deviation of actual output from its perfect credit market level. We explore various extensions, notably endogenous wages.