The theory of economics does not furnish a body of settled conclusions immediately applicable to policy. It is a method rather than a doctrine, an apparatus of the mind, a technique for thinking, which helps the possessor to draw correct conclusions.
Hard not to be struck by a parallel with Lukacs’s opening passage from History and Class Consciousness:
Let us assume for the sake of argument that recent research had disproved once and for all every one of Marx’s individual theses. Even if this were to be proved, every serious ‘orthodox’ Marxist would still be able to accept all such modern findings without reservation and hence dismiss all of Marx’s theses in toto – without having to renounce his orthodoxy for a single moment. Orthodox Marxism, therefore, does not imply the uncritical acceptance of the results of Marx’s investigations. It is not the ‘belief’ in this or that thesis, nor the exegesis of a ‘sacred’ book. On the contrary, orthodoxy refers exclusively to method. It is the scientific conviction that dialectical materialism is the road to truth and that its methods can be developed, expanded and deepened only along the lines laid down by its founders. It is the conviction, moreover, that all attempts to surpass or ‘improve’ it have led and must lead to over-simplification, triviality and eclecticism.
I’ve never had sympathy for what Lukacs says here, and don’t know the context for the Keynes quote. But I’m struck by the way that both Mankiw and Lukacs implicitly endorse the idea that they can just keep on keeping on, whatever happens in the actual world.