Thirlwall's law: binding constraint or ‘centre-of-gravity’?

Thirlwall's law is one of the most powerful empirical regularities in demand-led growth theories. In recent years, the challenges imposed by globalisation have led to a new wave of studies incorporating into this framework topics such as ecological sustainability, the complexity of innovation processes, the role of institutions, the composition of external imbalances, and gender issues. We notice some overlapping between two alternative interpretations: one that sees the law as a binding constraint and another that adopts a kind of ‘centre-of-gravity’ perspective. It is argued that they may be rather complementary. By means of a simple Keynesian multiplier model compatible with Harrodian instability, we show that assuming a balance-of-payments ceiling to growth gives rise to persistent and bounded fluctuations such that the external constraint works as an asymmetric ‘centre-of-gravity’. There is no need to impose a floor to output. Moreover, the model allows for different sources of autonomous demand. Numerical simulations show the robustness of our results with respect to alternative scenarios.