"Jacob Viner used to assign exam questions that showed how Ricardo’s Chapter 2 recognized (in modern parlance): P_2 / P_1 = \frac{\text{marginal cost in labour}_1}{\text{marginal cost in labour}_2} = \frac {1/\left[{\partial {Q}_/\partial{L}_}\right]}{1/\left[{\partial {Q}_/\partial {L}_}\right]} But, Viner insisted, this was compatible with rent’s being 99 per cent of national income and labour’s importance being derisory. Would that more historians of economic analysis had taken Viner’s EC 301 or brooded more on Ricardo’s text."