What has prompted me to write this note are the criticisms of a previous paper of mine (Kates 2018) by Alain Béraud and Guy Numa (2018; B&N hereinafter), which they subtitled “A Note on Kates, Grieve, and Ahiakpor.” “Kates,” they wrote, “is wrong” (B&N 2018, p. 285). And what was he wrong about? He had written, “Say’s Law states that recessions are never caused ... by demand deficiency” (ibid.; their ellipses). And what is particularly curious is that they have attributed to me the exact same understanding of Say’s Law that shows up in The General Theory. There was a time, perhaps half a century ago, that none of this would have had to be said. But let me state for completeness: according to John Maynard Keynes, because of their acceptance of some entity referred to by him as “Say’s Law,” classical economists had believed aggregate demand was always equal to aggregate supply so that recessions accompanied by mass unemployment were in theory never possible. The great divide between Keynesian macro and what came before is thus whether demand deficiency is a potential cause of recessions and mass unemployment. Virtually all economists today say it is. Virtually all economists prior to the publication of The General Theory said it was not. The issue, according to Keynes, was whether or not one accepted some entity he described as “Say’s Law.” On this, I hope we can all agree.

中文翻译：

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致编辑的信：萨伊法则：其起源和含义

促使我写这篇笔记的是对我的前一篇论文（Kate 2018）的批评，作者是AlainBéraud和Guy Numa（2018；下称B＆N），他们的副标题为“关于Kates，Grieve和Ahiakpor的笔记”。他们写道，“凯特斯是错的”（B＆N 2018，第285页）。他到底是怎么了？他曾写道：“萨伊定律指出，衰退绝不是由需求不足引起的”（同上；省略号）。尤其令人奇怪的是，他们将《通论》中对赛义定律的完全相同的理解归因于我。也许有半个世纪的时间了，所有这些都不必说了。但请允许我声明其完整性：根据约翰·梅纳德·凯恩斯（John Maynard Keynes）的说法，由于他们接受了他所称的“萨伊定律”，古典经济学家曾认为总需求总是等于总供给，因此从理论上讲，衰退和大规模失业是永远不可能的。因此，凯恩斯主义宏观经济与之前的巨大鸿沟是，需求不足是否会导致经济衰退和大规模失业。今天几乎所有的经济学家都这么说。在《通论》发表之前，几乎所有经济学家都表示并非如此。根据凯恩斯的说法，问题在于一个人是否接受了他所称的“说定律”。在此，我希望我们都同意。因此，凯恩斯主义宏观经济与之前的巨大鸿沟是，需求不足是否会导致经济衰退和大规模失业。今天几乎所有的经济学家都这么说。在《通论》发表之前，几乎所有经济学家都表示并非如此。根据凯恩斯的说法，问题在于一个人是否接受了他所称的“说定律”。在此，我希望我们都同意。因此，凯恩斯主义宏观经济与之前的巨大鸿沟是，需求不足是否会导致经济衰退和大规模失业。今天几乎所有的经济学家都这么说。在《通论》发表之前，几乎所有经济学家都表示并非如此。根据凯恩斯的说法，问题在于一个人是否接受了他所称的“说定律”。在此，我希望我们都同意。