Clower and Leijonjufjud reconstructed Keynes against the Keynesians - dynamic Keynesianism against static formal modelling - real time versus model time. They pointed to real-world experiences of changes in real time of prices and quantities produced by people acting on their disparate expectations. If incomes adjust rapidly - more rapidly than prices - an "income-constrained" process is possible. Production and employment may fall as a result of pessimistic expectations (loss of confidence, uncertainty) however produced.
My interpretation of real-world history suggests that this is not only logically coherent, it is also possible, and has happened from time to time. One may wonder whether the bounce-back of Keynesianism in the wake of the dot.com bust and the financial crisis, can be defended on the basis of this dynamic Keynesianism. On this I say the following.
1. Though one may see, if one looks hard enough, echoes of the Leijonhufjued-Clower reconstruction in the current climate of Keynesian opinion, it seems to me most of it is simply of the old ISLM, AS-AD variety, either explicitly, or else by implication inside the more sophisticated macro-models (stochastic or otherwise).
2. One may see in recent events evidence of income-constrained processes.
3. But this alone does not a Keynesian policy make. It is one thing to suggest that under some circumstances, the unsupported macro-economy may experience downturns. It is quite another to claim that, therefore, activist macro-policy is called for. There is no 'therefore' about it. Activist policy to be successful requires solutions to formidable knowledge and incentive problems. Failure to overcome these problems makes such policy destabilizing. And there is absolutely no attempt by the reborn Keynesians to grapple with this.
4. The conditions that produce significant income-constrained processes are worthy of examination, and, I would suggest are usually characterized by an accumulation of bad macro intervention policies - like artificially low interest rates, regulatory distortions on a macro scale (housing), etc.
5. Though income-constrained processes occur in the absence of policy distortions, they are likely to be relatively short-lived - quickly self-correcting. This is the empirical counterpart to recognizing the cogency of the argument while arguing against its significance in supporting activist, discretionary policy.
6. Non-Keynesians, Austrians and others, have not denied the possibility of income-constrained processes, like the 'secondary depression' that Hayek refers to. To claim that the unfettered market is basically stable, is not to claim that it is perfect, that it is free of all errors, or that adjustments to change are painless.