We may take as our unit for study an actual historical case of great dis-equilibrium, such as, say, the panic of 1873; or we may take as our unit for study any constituent tendency, such as, say, deflation, and discover its general laws, relations to, and combinations with, other tendencies. The former study revolves around events, or facts; the latter, around tendencies. The former is primarily economic history; the latter is primarily economic science.