Here is a tidbit I just found the end of R. G. Hawtrey’s long chapter on the General Theory in his volume Capital and Employment, (second edition, 1952) pp. 218-19.
Unemployment in Great Britain seemed at the time [1935 when Keynes finished writing the General Theory] to be chronic: the number of unemployed had never fallen below a million since 1921. Keynes was looking for an explanation of chronic unemployment, but it was hardly plausible to attribute it to the low long-term rate of interest [i.e., to a liquidity trap]. The yield of Government securities had been exceptionally high till the Conversion of 1932.
And in reality there is no school of thought for which the explanation of unemployment presents any difficulty. If wages are too high for full employment, and resist reduction, unemployment is bound to result. Adam Smith held that for a growing population a corresponding growth of capital was essential to maintain wages at or above subsistence level; the penalty for the failure of capital to grow was unemployment as well as starvation. For his successors it was self-evident that the employment afforded by the “wage fund” was inversely proportional to the rate of wages, and, when the theory of the wage fund was superseded by that of the marginal yield of labour, it was no less self-evident that a wage-level held above marginal yield would prevent full employment. Say’s loi des debouches declared that production generated its own demand; but if for any reason production was below capacity and there was unemployment, the demand generated would be no more than sufficient to absorb output at that level.
What I find especially interesting in the passage is Hawtrey’s correct understanding of Say’s Law, so that it constitutes not, as Keynes supposed, an assertion that unemployment is impossible, but an explanation of how aggregate demand is itself just the flip side of aggregate supply. Contractions of supply can be cumulative. It’s not just Keynesians who forget this essential point. RBC theorists and others who model the business cycle as a general-equilibrium phenomenon miss an essential feature of what constitutes the business cycle.