ABSTRACT. Gehrke et al. claim that Ricardo could only be criticized for having changed the definition of rent. Ricardo's theory of rent was tied directly to the marginal productivity of land. Formaini contends that Ricardo laid out the so-called law of diminishing returns as it applied to labor and capital: increasing the quantities of inputs will increase total production up to a point, but then output must decline, given that the land used is fixed in size. Peach affirms that the claim that the labor theory appealed to Ricardo because he thought it was a good empirical approximation is an inversion of the truth.