It well known that in multisector models of optimal growth, optimal paths converge to a unique steady state when future utilities are not discounted. Sutherland [1970], Kurz [1968], and Liviatan and Samuelson [1969] gave examples of multiple steady states when future utilities are discounted. Beals and Koopmans [1969] and Iwai [1972] used intertemporal utility functions, which also yield multiple steady states. The uniqueness of steady states with multiple consumption goods when future utility discounted has been studied by Brock [1973]. He showed tlhat if we assume that none of the goods are inferior in consumption (he calls this the normality condition for the utility function) the uniqueness of the steady state assured. Brock did not allow for pure consumption goods. Later Brock and Burmeister [1976] generalized Brock's result to allow pure consumption goods as well (Morishima [1974] type). Brock also formulated an alternative approach where uniqueness assured under the of a non-vanishing Jacobian for every non-negative discount rate. He writes however that the non-singularity of the Jacobian is an obscure assumption and that it would be worthwhile to relate it to the normality condition of the utility function. We first propose to weaken Brock's of non-vanishing Jacobian for every discount rate. Then in Section 3, Theorem 2, we show that the normality condition on the utility function implies a non-vanishing Jacobian. In Theorem 3 we weaken the normality condition for the uniqueness of the steady state by investigating the conditions for a non-vanishing Jacobian. We then clarify the economic content of our weaker conditions. In the final section we observe that the normality theorem can be proved for the joint production case (Mirrlees [1969] type) using a technique due to McKenzie [1963, 1973].
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