Tyler Cowen points us to a letter from Joan Robinson to a Marxist named Ronald Meek. There's a lot at the beginning criticizing Marxists for not understanding their own theory, but I found this section at the end particularly interesting. It presents a little bit of Robinson's understanding of Keynes's place in the history of economic thought:
"Ricardo existed at a particular point when English history was going round a corner so sharply that the progressive and the reactionary positions changed places in a generation. He was just at the corner where the capitalists were about to supersede the old landed aristocracy as the effective ruling class. Ricardo was on the progressive side. His chief pre-occupation was to show that landlords were parasites on society. In doing so he was to some extent the champion of the capitalists. They were part of the productive forces as against the parasites. He was pro-capitalist as against the landlords more than he was pro-worker as against capitalists (with the Iron Law of Wages, it was just too bad for the workers, whatever happened).
Ricardo was followed by two able and well-trained pupils – Marx and Marshall. Meanwhile English history had gone right round the corner, and landlords were not any longer the question. Now it was capitalists. Marx turned Ricardo’s argument round this way: Capitalists are very much like landlords. And Marshall turned it round the other way: Landlords are very much like capitalists. Just round the corner in English history you see two bicycles of the very same make – one being ridden off to the left and the other to the right.
Marshall did something much more effective than changing the answer. He changed the question. For Ricardo the Theory of Value was a means of studying the distribution of total output between wages, rent and profit, each considered as a whole. This is a big question. Marshall turned the meaning of Value into a little question: Why does an egg cost more than a cup of tea? It may be a small question but it is a very difficult and complicated one. It takes a lot of time and algebra to work out the theory of it. So it kept all Marshall’s pupils preoccupied for fifty years. They had no time to think about the big question, or even to remember that there was a big question, because they had to keep their noses right down to the grindstone, working out the theory of the price of a cup of tea.
Keynes turned the question back again. He started thinking in Ricardo’s terms: output as a whole and why worry about a cup of tea? When you are thinking about output as a whole, relative prices come out in the wash – including the relative price of money and labour. The price level comes into the argument, but it comes in as a complication, not as the main point. If you have had some practice on Ricardo’s bicycle you do not need to stop and ask yourself what to do in a case like that, you just do it. You assume away the complication till you have got the main problem worked out. So Keynes began by getting money prices out of the way. Marshall’s cup of tea dissolved into thin air. But if you cannot use money, what unit of value do you take? A man hour of labour time. It is the most handy and sensible measure of value, so naturally you take it. You do not have to prove anything, you just do it.
Well there you are – we are back on Ricardo’s large questions, and we are using Marx’s unit of value. What is it that you are complaining about?
Do not for heaven’s sake bring Hegel into it. What business has Hegel putting his nose in between me and Ricardo?"
The bolded section was very strange to me and I had to look back to Keynes's chapter on the choice of units. He says pretty clearly that he's using two units - "labor units" and "money value". Now perhaps she just means that in applications he divides one by the other, in which case that's OK. But the way she says it (particularly what she says at the end) sounds an awful lot like she's suggesting Keynes is using a labor theory of value.