There is also present another source of energy operating in a more continuous fashion and being more intimately connected with the permanent evolutio… - 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.

Two important features in the modern development of economics are the application of mathematics to abstract economic reasoning... and the attempt at placing economics on a numerical and experimental basis by an intensive study of economic statistics.

In reality the cycles we have the occasion to observe are generally not damped. How can the maintenance of the swings be explained? Have theses dynamic laws deduced from theory and showing damped oscillations no value in explaining the real phenomena, or in what respect do the dynamic laws need to be completed in order to explain the real happenings? They (dynamic laws) only form one element of the explanation: they solve the propagation problem. But the impulse problem remains.