Comment: Hayes on Z
评论海耶斯对凯恩斯总供给函数Z的解读，指出其强调产出异质性的贡献，但质疑其认为凯恩斯拒绝总量概念的极端观点。
Mark Hayes's contribution (Hayes, 2007) is to be welcomed as it reaffirms that the economics of Keynes, which is sometimes denounced as being restricted to the demand side, has a solid supply-side basis in Keynes's ‘Aggregate Supply Function’, Z. Of course, Hayes is not the first scholar to stress this. Roberts (1978), Koenig (1980), Amadeo (1989), Palley (1997) and others have pointed out that Keynes's acceptance of the ‘first classical postulate’ (Keynes, 1973, pp. 17−8) implies the adoption of the neo-classical supply-side assumptions of price-taking, profit-maximisation and decreasing marginal returns to labour. What distinguishes Hayes's contribution from this literature is his emphasis on the heterogeneity of output. Hayes reminds us that Keynes, in the General Theory (1973, pp. 38−40), expresses his unease with the concepts of aggregate levels of prices and output. Yet to claim that Keynes was ‘adamant’ that these concepts were ‘inadmissable’, as Hayes does (2007, p. 1), would, in our view, mean to throw out the baby with the bathwater. The notions of aggregate output (real gross or net domestic product) and the price level are very useful for macro-analysis, and Keynes adopts them in chapters 20 and 21 (and also at the end of chapter 15) of the General Theory without a second thought—as Hayes admits himself in footnote 1 on page 10 of his article. In fact, it would be hard to understand why Keynes is widely praised as the founder of macroeconomics if he really held the opinion that concepts such as gross domestic product were ‘inadmissable’.