“It seems to me that economics is a branch of logic, a way of thinking; and that you do not repel sufficiently firmly attempts à la Schultz to turn it into a pseudo-natural-science. One can make some quite worthwhile progress merely by using your axioms and maxims. But one cannot get very far except by devising new and improved models. This requires, as you say, “a vigilant observation of the actual working of our system”. Progress in economics consists almost entirely in a progressive improvement in the choice of models. The grave fault of the later classical school, exemplified by Pigou, has been to overwork a too simple or out of date model, and in not seeing that progress lay in improving the model; whilst Marshall often confused his models, for the devising of which [b] he had great genius, by wanting to be realistic and by being unnecessarily ashamed of lean and abstract outlines.”
“Economics is a science of thinking in terms of models joined to the art of choosing models which are relevant to the contemporary world. It is compelled to be this, because, unlike the typical natural science, the material to which it is applied is, in too many respects, not homogeneous through time.”
http://economia.unipv.it/harrod/edition/editionstuff/rfh.346.htm
Interesting stuff, interesting stuff.