Unlearningecon quotes Keynes, showing the latter pre-empted Sumner by about 70 years,
But if our central controls succeed in establishing an aggregate volume of output corresponding to full employment as nearly as is practicable, the classical theory comes into its own again from this point onwards.
— John Maynard Keynes,The General Theory (BN Publishing, 2008), p. 378.
One commentator on Unlearningecon’s blog locked on Keynes’ emphasis on full employment. I think “full employment,” in the context of Keynes, should be assumed to be synonymous with “effective demand” — this is the essence of chapter four.