A continuación un fragmento del capítulo 8 del libro "Piero Sraffa" de Alessandro Roncaglia, donde plantea las dos distintas concepciones de competencia, una para la economía clásica, otra para la economía neoclásica:
"The assumption of a uniform rate of profits in the various sectors thus reflects the classical and Marxian conception of competition based on freedom of entry of new firms into each productive sector. Under such conditions it is, in fact, impossible for any single sector to realise continuously an above-average rate of profits, for new firms would be attracted into the sector in question by the possibility of earning higher profits. As a consequence, productive capacity and supply would rise relative to demand, putting a downward pressure on prices (and vice versa in the case of a rate of profits below the average). This type of competition bears little relation to any particular firm’s ability to set the price of its own product. Nor is it related to the size of any individual firm as a proportion of the entire industry. The only necessary conditions are that technological discontinuities related to a minimum plant size do not play a relevant role, and that legal (and more generally, institutional) obstacles to the free movement of capital between sectors do not exist, so that no barriers to entry exist for new (potential) producers."