Economic Growth, the Mathematical Pendulum, and a Golden Rule of Thumb

It is argued that due to their general instability dynamic optimization models cannot be used as positive theories of economic growth. The argument is substantiated by (numerical) examples. A simple rule of thumb is provided as an alternative to the RKC model. This rule is shown to perform well from a normativeand to be reasonable from a positive point of view. The model is consistent with empirically estimated rates of convergence if a broad concept of capital is used.