The broadest classification of the theories presented by Haberler was twofold: monetary and real. Under each category were theories emphasizing different aspects of the economy as well as mixed theories that attempted to incorporate factors from one category into a theory emphasizing the other. The causal focus from the monetary point of view was on the quantity of money and its velocity (transactions or income velocity). The general idea was that an increase in MV accompanied rising physical output and employment while a decrease was associated with the reverse effect. However, in a prescient footnote, Haberler added: “It is conceivable that the rise and fall of the volume of production might be accompanied by an opposite movement of prices.” (Haberler [1936] 1939, 14, f.2) In general, writers on the monetary aspects stressed the familiar factors of bank credit conditions, interest rates, and price level changes. This led to consideration of central bank policy and to the “rules” of sound banking under the gold standard, this latter institution being largely moribund by 1936, but not expected to remain so.