Generalizing the permanent-income hypothesis: Revisiting Friedman’s conjecture on consumption

Friedman’s contribution to the consumption literature goes well beyond the seminal permanentincome hypothesis. He conjectured that the marginal propensity to consume out of financial wealth shall be larger than out of ‘‘human wealth’’, the present discounted value of future labor income. I present an explicitly solved model to deliver this widely noted consumption property by specifying that the conditional variance of changes in income increases with its level. A larger realization of income not only implies a higher level of human wealth, but also signals a riskier stream of future labor income, inducing a higher precautionary saving, and thus giving rise to Friedman’s conjecture. Appropriately adjusting human wealth for income risk, I show that Friedman’s conjecture may be formulated as a ‘‘generalized’’ permanent income hypothesis. I further show that Friedman’s conjecture captures the first-order effect of stochastic precautionary savings. Finally, I propose a natural decomposition of the optimal saving rule to formalize various motives for holding wealth as emphasized in [Friedman, M., 1957. A Theory of the Consumption Function. Princeton University Press, Princeton]. r 2006 Elsevier B.V. All rights reserved.