political or physical type. About the relative importance of the forces which produce divergencies among business cycles, however, and about their interactions, our knowledge is meager. Perhaps we are overlooking forces which will some day be found to play dominating rôles. But the way to hasten the day of fuller understanding is to make the best use we can of our present insights, imperfect though they are.
Taken one at a time, most of the theories of business cycles reviewed in Chapter I seem plausible, not to say convincing. Certainly each theory, this time without exception, illuminates some angle of the problem. Taken all together, the theories render a different service--one which is welcome only to the man who has the courage and time to enter upon a thorough investigation. They show that business cycles are congeries of diverse fluctuations in numerous processes--physical, psychological, and economic. Indeed, upon reflection the theories figure less as rival explanations of a single phenomenon than as complementary explanations of closely related phenomena. The processes with which they severally deal are all characteristic features of the whole. These processes not only run side by side, but also influence and (except for the weather) are influenced by each other. Thus the diversity of explanations, which at first seems confusing, becomes an aid toward envisaging the complex character of the problem.
Complexity is no proof of multiplicity of causes. Perhaps some single factor is responsible for all the phenomena. An acceptable explanation of this simple type would constitute the ideal theory of business cycles from the practical, as well as from the scientific, viewpoint. But if there be one cause of business cycles, we cannot make sure of its adequacy as an explanation without knowing what are the phenomena to be explained, and how the single cause produces its complex effects, direct and indirect. Neither on the single-cause hypothesis, nor on the hypothesis of multiple causes, are we equipped to deal with the problem of causation until we have learned what are the processes characteristic of business cycles, and how these processes are related to one another. Chapter I indicated what the leading proc