Retrospectives: Say's Law

What is perhaps most curious about 'Say's law' is the continuing disagreement on its substance and to whom it should be credited. John Maynard Keynes summarized the law as 'supply creates its own demand' but it is now generally agreed that Keynes did not get it quite right. The author has been unable to ascertain who coined the term 'Say's law' but it appears to be a twentieth century appellation, preceding Keynes's use. John-Baptiste Say was certainly among the earlier writers to discuss the topic at length but so far as the author can determine, none of Say's contemporaries--including Say himself--credits him with having been first to enunciate its principles.