The term ‘Keynesian economics’ means different things to different people. But one thing almost everyone can agree on is that Keynesians believe that the 2009 fiscal stimulus boosted aggregate demand, at least compared to the no-stimulus alternative. Alternatively, Keynesians believe the fiscal multiplier is positive. In my view that’s a sort of sine qua non of modern Keynesianism. Yes, it has many other things to say, but without the fiscal multiplier there’s nothing particularly “Keynesian” about the rest of the theoretical apparatus.