repeated, this time with the ith exchange rate constant, we would get, instead of (7),
and the stability condition Deltaii / Deltaii,rr< 0, which is one of the Hicksian conditions of perfect stability. Proceeding along these lines, holding one or another set of prices constant, we get the complete Hicks conditions of perfect stability.
But does this dynamic process have any economic plausibility ? Are we not, as Samuelson argued, allowing "arbitrary modification of the dynamical equations of motion"? The answer is, in a sense, yes. But this can be the exact method needed in the theory of policy, where our purpose is to design stable dynamic systems.
As an example, we might be interested in examining aspects of the stability of an exchange-rate system such as that recently advocated by sixteen distinguished academic economists  -a sliding parity system (with widened exchange-rate margins).9 Is it not precisely a set of conditions such as the Hicks conditions that would be involved? We might ask, first, what would happen if, say, Britain (which we shall identify with country 1) adopted a sliding parity system while a subset of other countries (2, . . ., j) allowed their exchange rates to float, and the remaining countries, k, . . ., n, kept their rates pegged to, say, the U.S. dollar (the currency of country 0). Then, if we suppose that balances of payments of countries whose rates float adjust instantaneously while the pound adjusts slowly, the path of the pound over time would be
for which knowledge of the Hicks conditions would be directly relevant. Thus the particular form of the dynamic system adopted -which countries are left out and which are left in- would depend on which of the Hicks conditions are satisfied. The Hicks method does, therefore, have a role to play in dynamic aspects of the theory of economic policy.
The Hicks conditions, however, are not exactly what we need for the theory of economic policy, because, as we shall see, they are incomplete even in terms of Hicks' own method. In the experiments