Two important features in the modern development of economics are the application of mathematics to abstract economic reasoning... and the attempt at… - Ragnar Frisch

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.

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.

Econometrics is by no means the same as economic statistics. Nor is it identical with what we call general economic theory, although a considerable portion of this theory has a definitely quantitative character. Nor should econometrics be taken as synonymous with the application of mathematics to economics. Experience has shown that each of these three view-points, that of statistics, economic theory, and mathematics, is a necessary, but not by itself a sufficient, condition for a real understanding of the quantitative relations in modern economic life. It is the unification of all three that is powerful. And it is this unification that constitutes econometrics.