The Keynesian models fundamentally divorce consumption spending from investment spending. In the work of the early pioneers of neoclassical theory (Walras, Jevons, Menger, Clark, Marshall, Pareto), decisions to invest meant decisions that ultimately led to the production of consumer goods. Some consumer goods could be produced directly but the vast majority required the prior production of capital goods. Thus, real investment typically meant the production of capital goods at one link in a supply chain with the help of capital goods that had already been produced at another link in the supply chain that was "farther away" from the ultimate consumer good. The idea of "investing" without there being supply chains would have been unthinkable to the general equilibrium, marginal productivity theorists of the late 19th and early 20th century. I am amazed when I reflect on the fact that Keynesian macroeconomics is built on a foundation that almost completely disregards this most important idea. In this field, the decision to produce capital goods is completely disconnected from the decision to produce consumption goods. Similarly, there is virtually no connection between the early general equilibrium theory of the neoclassicals mentioned above and the later Keynesian macro. Arguably the most important lesson in economics since Adam Smith's invisible hand was expunged from the "science" and generations of "macroeconomics" students were trained as if it had never existed. The reason why I object to AD/AS analysis being taught in the principles classroom and to IS/LM being taught in the intermediate and graduate texts is that it amounts to a retrogression. To teach this is, to me, analogous to burning the libraries at Alexandria as opposed to learning from them. To carry the analogy a step farther, I regard it as part of a dark age in the history of economics. Pat Gunning