On sustained economic growth with wealth effects

In a discounted one-sector convex model of optimal economic growth where utility may depend on both consumption and capital stock, I derive necessary and sufficient conditions for sustained growth (unbounded expansion of capital and consumption). Conditions for bounded growth and extinction are also outlined. Optimal paths may be non-monotone. Sustained growth may occur even though the asymptotic marginal productivity is less than the discount rate and may require the initial capital stock to be above a critical level. The behavior of the marginal rate of substitution between consumption and capital plays a crucial role in the conditions.