Joan Robinson, Cambridge University
On page 104, she offers a frank comment on marginal productivity theory:
There is the problem of the relative levels of different types of earned income. Here we have the famous marginal productivity theory... The real wage of each type of labour is supposed to measure its marginal product to society. The salary of a professor of economics measures his contribution to society and the wage of a garbage collector measures his contribution. Of course this is a very comforting doctrine for professors of economics but I fear that once more the argument is circular. There is not any measure of marginal products except the wages themselves. In short, we have not got a theory of distribution. We have nothing to say on the subject which above all others occupies the minds of the people whom economics is supposed to enlighten.Ouch!