 stability on the grounds, as stated above, that "stability conditions are not deduced from a dynamic model, except implicitly." Hicksian stability is not equivalent to "true" dynamic stability, and the Hicks conditions are neither necessary nor sufficient for the convergence of the dynamical system implicit in Hicks' dynamics, that is, the dynamic system Samuelson postulated as the "natural extension" of the Walrasian system. True dynamic stability requires that the roots of the characteristic equation of the dynamic system have negative real parts, and this requirement is not equivalent to the Hicks conditions.5
Samuelson's criticism undermined the logic of Hicks' method. But the conditions of stability produced by that method retained an important place in the literature. Samuelson had already observed that the Hicks conditions were equivalent to the conditions of "true" dynamic stability in the symmetrical case. Metzler showed that they were equivalent in the case of gross substitutes, and also necessary (but not sufficient) for stability to be independent of the speeds of adjustment (Metzler ).6 Morishima proved that they were equivalent for certain classes of complements. They are also sufficient conditions for convergence of any nonoscillating system, since Hicksian (perfect) stability implies the absence of positive real roots. They are, moreover, conditions that, if not satisfied, yield anomalous comparative statics results, and thus seem at least to be necessary conditions for useful applications of the correspondence principle, at least in the context of analysis of the Walrasian system. Thus, even though Hicks' method seems to lack theoretical justification,7 the Hicks stability conditions produced by that method have proved exceedingly useful.
How can a wrong method yield useful results ? Leaving aside coincidence, the answer may lie in the two-way character of the correspondence principle. Samuelson  had observed that
not only can the investigation of the dynamic stability of a system yield fruitful