 The idea that workers have rights to the contributions their labour makes to the production of a social surplus is, we noted, common to both Marxist and Libertarian theories. Yet, the widespread rejection of the labour theory of value apparently undermines (Cohen’s arguments notwithstanding) of Marx’s classical account of exploitation. Neoclassical economists subsequently developed an account of exploitation that incorporates this concern for an input’s contribution to the productive surplus that is compatible with the subjective theory of value that replaced labour theories in mainstream economic thinking. This account claims “a factor of production is exploited if it is employed at a price which is less than its marginal net productivity” (Robinson 1933: 281).