Profits are key to capitalist investment, not ‘effective demand’ as Keynesians argue, or changes in interest rates or money supply as Monetarists and the Austrian school argue. I differ strongly from the post-Keynesian view that profits are a ‘residual’ generated by investment; or as Keynesian-Marxist Michal Kalecki put it: ‘capitalists earn what they invest, while workers spend what they earn’.