SEMAINE D'ÉTUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIQUE ETC. 23C

Hence (13) expresses equality, at all times #, of the marginal
productivity of capital (in producing capital, say) to the growth
rate A — a prescription known as the golden rule of accumulation
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1G

6. EXISTENCE AND CHARACTERISTICS OF OPTIMAL PATHS

We now return to the original problem that allows x, and z,
to vary in time and recognizes the restriction (10 d) of a historically
 given initial capital stock, and look about for a suitable
maximand. We admit to an ethical preference for neutrality
as between the welfare of different generations. After some
hesitation, we tentatively and arbitrarily resolve another ethical
conundrum by interpreting this « timing neutrality » in a percapita
 sense. That is, we assume first of all that labor force
and population grow in proportion. Furthermore we thus imply

(") PHELPS [1061

+1 Koopmans - pag. 15