Fisher's main intellectual rival was the Swedish economist Knut Wicksell. Fisher espoused a more succinct explanation of the quantity theory of money, resting it almost exclusively on long run prices. Wicksell's theory was considerably more complicated, beginning with interest rates in a system of changes in the real economy. Although both economists concluded from their theories that at the heart of the business cycle (and economic crisis) was government monetary policy, their disagreement would not be solved in their lifetimes, and indeed, it was inherited by the policy debates between the Keynesians and monetarists beginning a half-century later.