Beyond the linearity critique: the knife-edge assumption of steady-state growth

The "linearity critique" of endogenous growth models is presented in a general context of an arbitrary growth model and reassessed. It is argued that presence of linearities is not a valid criterion for rejecting growth models. Existence of exponential/geometrical steady-state growth (i. e. of a balanced growth path with strictly positive growth rates) necessarily requires some knife-edge condition which is not satisfied by typical parameter values. Hence, balanced growth paths are fragile and sensitive to smallest disturbances in parameter values. Adding higher order differential/ difference equations to a model does not change the knife-edge character of steady-state growth.