Steve Kates, First of all, I do not think that introducing explicitly AS and AD is all that Keynes did. But, I accept that he may well be credited with having done that, and I think that is worthwhile, even if you do not. Regarding the Great Depression, I am more on your side than most are regarding the role of the Smoot-Hawley tariff. I can also see that this might be argued to be at least somewhat, if not entirely, a supply-side phenomenon. However, it is clearly not all that was going on, and you do not claim that it was. Your other factor is rising interest rates, which I would agree with, although I would add the further subsequent collapse of financial markets more generally, which was not entirely due to the rise in interest rates. However, the question that arises here is whether or not this is a matter strictly of aggregate supply or not. You make much of the issue of whether effects are coming from investment or consumption and somehow argue that the first have nothing to do with AD. But, while investment eventually leads to a change in AS the capital stock increases, the process of building capital stock, the act of real capital investment, involves demand for the machinery and construction and so forth that is involved. It is a parrt of AD just as much as G or X or C are. Keynes clearly emphasized fluctuations of I as key to AD fluctuations leading to macro fluctuations. He did not write or speak of "business hitting the limit of what can be profitably invested." No, he emphasized fundamental uncertainty and irrationality, with ultimately psychological factors playing the key role, "animal spirits," which lie behind the willingness of business people to carry out capital investments. If their animal spirits collapse, perhaps inspired by a collapse of the financial sector, then their reduced capital investments reduce AD leading to negative multiplier effects that operate through consumption, and so forth. So, I do not see your argument as at all disproving the role of AD in bringing about the Great Depression or showing Keynes's analysis to be incorrect. Regarding the role of fiscal policy, I note that content of it matters. Thus, some public works are actually public capital infrastructure that can improve the future productivity of the economy, e.g. the autobahnen of Germany. Assuredly there are make-work and pork barrel infrastructure spending projects that rare wasteful. But some of this kind of spending is actually capital investment in a real sense, even if we do not count it as such in the official income and product accounts used in most market capitalist economies. Just as with private capital investment, such spending will have the dual aspect of stimulating AD in the short run while shifting out AS in the longer run, at least from the perspective of us who think that thinking in terms of AS and AD is not a complete absurdity and waste of time and intellectual effort. Finally, I am glad that you do indeed recognize that Say did not always fully accept his own law, as he did allow for the possibility of hoarding. You note this by dismissing Say for his supposedly inferior awareness of the glorious truth of his own law. Of cause the person who really crystallized and publicized his law was not John Stuart Mill, but his father, James, who coined the term "supply creates its own demand," just to get back to the HET aspect of this. Ricardo got it from him and even called it "Mill's Law" at some point or other. You may be right that the term "Say's Law" did not appear until the 1920s, but I simply do not know about that one way or the other. Of course J.S. Mill followed his father and vigorously denied the possibility of "general gluts," ascribing recessions most often to financial collapses often following speculative bubbles. Now, I have discussed above how financial collapses can easily be analyzed as a source of collapsing aggregate demand as businesses fail to carry out real capital investments, which then, well, I shall not repeat what I said above. In any case, Mill's argument ultimately was one about the long-run, but clearly in the short run there could be these disruptions of capital investment that a Keynesian could easily trace out as bringing about the recession (in the short run) due to insufficient AD. Besides Malthus, other classical economists who accepted the idea of the possibility of a "general glut" were Sismondi as early as 1819, and Marx, who in Volume III of Capital specifically criticized the argument of J.S. Mill. Barkley Rosser