A few general statements can be made about the development of business cycle theories: First, they had always been dynamic theories. They began with a recognition of the fact of continual change in the overall economy. Further, they were historical theories. There was a basic assumption that whatever economic conditions are today, they are, at least in part, the result of the past history of the economy, especially the history of the recent past. Finally, almost all who worked on the problem were attracted by the idea that there was a periodicity in terms of calendar time to the various aspects of the cycle.