Jonathan considers the question.
The Keynesianism we have is really Hicksianism. I do think economists appreciate this. I think most economists know IS-LM as we use it is not in the General Theory (of course you can yank it out of there if you wish, but be prepared to get nagged by some post-Keynesians). So of course the Keynesianism that grew out of IS-LM great out of Hicks (for the rest of this post though, when I talk about Keynesianism I'll be referring to old Keynesianism/IS-LM not the newer stuff).
So if we know this why do we still praise Keynes?
This is going to sound a little fuzzy, but I think it's because Keynes taught us how to think about things and Hicks taught us how to model things. Those are two very different tasks, and it's the former task that tends to loom large in our psyches. When we want to walk someone through the logic of a Keynesian answer to a question, we always go back to the props that the General Theory furnishes us with. The catchy passages in the book don't hurt - many people have pointed this out. But I don't think it's just that. It's how compelling the argument is. Hicks doesn't give us anything like this sort of intuitive argument that we can whip out when we need it. He gives us the model. The model is important, but it doesn't frame the theory the way Keynes does.
As an example of what I mean, think about the theory of the Phillips Curve or the NAIRU. These are big ideas associated with Phillips and Friedman, respectively. That's because they presented us with the idea and when we think about the idea we're drawn back to their exposition of the idea. But lots and lots of people have modeled the Phillips Curve and the NAIRU - some models explaining the same phenomenon but with strikingly different explanations. Some models are constructed differently but give us basically the same story. A model is just a bit of math to illustrate a concept - it's smaller than a "theory". You can have lots of different models of the same theory.
Now Hicks's model was a big deal. But I think Keynes still looms large because he ultimately gave us the concept of Keynesianism.
I would be careful not to understate Keynes's contribution, though. Liquidity preference theory of the interest rate is essentially original to him (you can find wisps of antecedents in Franklin and Fisher), and it's actually one that Hicks was skeptical of early on (Hicks referred to it as seeming like interest rates were being pulled up by their own bootstraps). I think the fact that we have preferred the Hicksian version of liquidity preference is that his exposition is more Marshallian than Keynes's (which gives us this nebulous idea of lots of potential states of the economy). Keynes wanted to present a picture of multiple potential states - an unclosed model - because he was presenting an alternative to the idea (we can argue about how prevalent it was) that the economy is always going to be operating at full employment or at least tending towards it. That view of things - that model of the bigger idea - didn't last as the model that we use to represent the bigger idea, because most of us are more comfortable with closed models and unique equilibria.
Keynes also has a lot of good substantive contributions that are simply left unexploited by mainstream economists and have been taken up by heterodox economists.
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