Nine-tenths of the economic fallacies that are working such dreadful harm in the world today are the result of ignoring this lesson. Those fallacies all stem from one of two central fallacies, or both: that of looking only at the immediate consequences of an act or proposal, and that of looking at the consequences only for a particular group to the neglect of other groups.
It is true, of course, that the opposite error is possible. In considering a policy we ought not to concentrate only on its long-run results to the community as a whole. This is the error often made by the classical economists. It resulted in a certain callousness toward the fate of groups that were immediately hurt by policies or developments which proved to be beneficial on net balance and in the long run.
But comparatively few people today make this error; and those few consist mainly of professional economists. The most frequent fallacy by far today, the fallacy that emerges again and again in nearly every conversation that touches on economic affairs, the error of a thousand political speeches, the central sophism of the new economics, is to concentrate on the short-run effects of policies on special groups and to ignore or belittle the long-run effects on the community as a whole. The “new” economists flatter themselves that this is a great, almost a revolutionary advance over the methods of the “classical” or “orthodox,” economists, because the former take into consideration short-run effects which the latter often ignored. But in themselves ignoring or slighting the long-run effects, they are making the far more serious error. They overlook the woods in their precise and minute examination of particular trees. Their methods and conclusions are often profoundly reactionary. They are sometimes surprised to find themselves in accord with seventeenth-century mercantilism. They fall, in fact, into all the ancient errors (or would, if they were not so inconsistent) that the classical economists, we had hoped, had once and for all got rid of.