Irving Fisher on the business cycle

6. There are two sorts of cyclical tendencies. One is "forced" or imposed on the economic mechanism from outside. Such is the yearly rhythm; also the daily rhythm. Both the yearly and the daily rhythm are imposed on us by astronomical forces from outside the economic organization; and there may be others such as from sun spots or transits of Venus. Other examples of "forced" cycles are the monthly and weekly rhythms imposed on us by custom and religion. The second sort of cyclical tendency is the "free" cycle, not forced from outside, but self-generating, operating analogously to a pendulum or wave motion.

7. It is the "free" type of cycle which is apparently uppermost in the minds of most people when they talk of "the" business cycle.

~ Irving Fisher, "The Debt-Deflation Theory of Great Depressions," September 1933