This theory is set forth with the qualification that these effects are the "normal" effects of the changes in question. The proportion between quantity of money and price-level is not strictly maintained during "transition periods." I now approach the most difficult question which I shall have to answer as to the meaning of Fisher's terms. The same problem arises for all quantity theorists. Precisely what is the distinction between "transition periods" and "normal periods"? What limitations and qualifications does he admit to the rigorous statement of his theory so far given? I may first express the opinion that the line shifts greatly in his own mind, or at least shifts greatly in the exposition. I do not find an explicit statement in which definitions are given. The matter is chiefly discussed by Fisher in ch. 4,[184] which is called "Disturbance of Equation and of Purchasing Power during Transition Periods." There we find, as I have stated, no definitions, but the initial statements would suggest the following: a transition period is the period following a change in any one of the factors in the equation during which a readjustment among all the others is taking place; the normal period is the period preceding such a change, or following the transition after such a change, and is characterized by the fact that all the factors are at rest, in stable equilibrium. Equilibria during transition periods are unstable. During the transition, the relations among the factors vary: M and M' need not keep their fixed ratio; P need not be wholly passive; M and P need not keep the same proportion. But until M and M' get back into the normal ratio, until P becomes proportional to M (in the proportion prior to the initial disturbance), there is no rest; the equilibrium is unstable. How long is a transition period? How realistic is the notion of a transition period? Is the transition period a theoretical device, to aid in isolating causes, or is it supposed to be a real period in time? Is the normal period a real period in time, or is it merely a theoretical hypothesis? It is not easy to answer these questions. Thus (p. 72) the seasonal fluctuations are declared to be "normal and expected," and, at the same time, one gets the impression that Fisher considers them illustrations of his "transitions," in which the normal theory does not strictly hold (pp. 72, 169). What is described chiefly in the chapter on transition periods is the business cycle--a theory of the business cycle, based primarily on the notion that the failure of interest to rise as fast as prices rise causes the "boom," and that the draining of bank reserves precipitates the crisis. I shall not discuss this theory, as a theory of business cycles, further than to say that Wesley Mitchell's study would indicate that the interest rate is a minor factor, and that, while as a theoretical possibility, the drains on bank reserves may check prosperity if something else doesn't do it first,