6. The basic classical model can account for the procyclical and leading behaviour of money if there is reverse causation, that is, if anticipated changes in output lead to changes in the money supply in the same direction. For example, if firms increase their money demand in anticipa- tion of future output increases, and if the cen- tral bank (to keep the price level stable) supplies enough extra money to meet the increase in money demand, increases in the money stock precede increases in output. This result holds even though changes in the money stock do not cause subsequent changes in output.