Usually it is easier to obtain estimates for budget proportions and Engel elasticities than for elasticities with respect to price. By making certain… - Ragnar Frisch

Questions of convergence under an infinite time horizon will depend so much on epsilontic refinements in the system of assumptions — and on the infinite constancy of these refinements — that we are humanly speaking absolutely certain of getting infinite time horizon results which have no relevance to concrete reality. And in particular we are absolutely certain of getting irrelevant results if such epsilontic exercises are made under the assumption of a constant technology. 'In the long run we are all dead.' These words by Keynes ought to be engraved in marble and put on the desk of all epsilontologists, in growth theory under an infinite horizon.

Certain exterior impulses hit the economic mechanism and thereby initiate more or less regular oscillations.

I believe that economic theory has arrived at a point in its development where the appeal to quantitative empirical data has become more necessary than ever. At the same time its analyses have reached a degree of complexity that require the application of a more refined scientific method than that employed by the classical economists.