The majority of the economic oscillations which we encounter seem to be explained most plausibly as free oscillations. - Ragnar Frisch

There is also present another source of energy operating in a more continuous fashion and being more intimately connected with the permanent evolution in human societies.

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.

I have insisted that econometrics must have relevance to concrete realities, otherwise it degenerates into something which is not worthy of the name econometrics, but ought rather to be called playometrics.