Dynamic optimisation problems involving rational expectations require a transversality condition to produce a unique solution (see Hall, Henry and Wren-Lews, 1986, for an example). These transversality conditions generally amount to a statement about the nature of the endogenous variable in the infinite Song run; for example, that the long run involves a stable equilibrium. An analagous problem arises in econometric macro models, where a unique solution requires a ‘terminal condition’ for any forward-looking variables beyond the solution period of the model. Transversality and terminal conditions are not equivalent, however, because we cannot solve macro models into the infinite future (see Hall and Henry, 1988, pages 192-198).