Stability issues, although a typical preoccupation of dynamic policy analysis, have so far not figured centrally in the current analysis of the dynamic theory of policy. Such issues were, it is true, but thinly disguised in the previous chapter as the correspondence of existence for the asymptotic flexible objective problem with the stability of the preference variables. Elsewhere Section 9.7 referred briefly to the property of instrument instability in the fixed target problem, promising to reconsider that phenomenon jointly with the flexible objective problem.

This final chapter not only redeems that promise but also explicitly considers a miscellany of stability questions pertinent to the asymptotic flexible objective problem when existence, pursued so vigorously in Chapter 12, is not the sole concern. The concentrated rigour of that chapter is deliberately counterbalanced here by a more discursive and leisurely approach: for relevant stability issues are too numerous to allow more than a broad-brush analysis. But the analytical policy framework evolved in the preceding chapters will, when required, readily permit sustained analysis of those issues only adumbrated here.

Verification of the existence of an optimal policy for a particular preference specification is typically only part of the process of designing an optimal policy; for it may also be necessary to alter the preference specification before the optimal policy is adjudged fully satisfactory. Indeed, optimal policies are no better than the policy model permits and the preference specification insists; and this tension between positive capability and normative compulsion is accordingly the theme of this final chapter.