The Varieties of Subjectivism: Keynes and Hayek on Expectations

J.M. Keynes and F.A. Hayek had different economic ideas even though both were subjectivists seriously engaged with issues of time and uncertainty in economics. The source of the difference between their economic ideas was the difference between their philosophical ideas. Keynes was a Cartesian rationalist and justificationist; Hayek a critical rationalist and non-justificationist. We draw on Keynes's "A Treatise on Probability," Hayek's "The Sensory Order," and other works to defend our argument. Although Keynes and Hayek might both be called "subjectivists," there are varieties of subjectivism. Their subjectivist ideas are not fully compatible with one another and conduce to different theories of the market process. Hayek's theory, not Keynes's, allows us to say when markets will behave in the way Keynes described and when they will instead behave in more coordinated ways. In this sense, a Hayekian theory is needed to understand a Keynesian world.