Milton Friedman - Capitalism and Freedom, p. 135

Note to self: if this is true, then Sraffa was incorrect in taking the rate of profits rather than the wage rate (à la Ricardo) as exogenous. Besides this, however (which was something of an arbitrary choice to begin with), this relation would not contravene Sraffa’s theory of prices, but would submit it to a different determination-in-the-last-instance (viz. quantity of money, though this may be further reducible). Optimally, this modification will serve to eliminate agency even further from Sraffa’s theory, allowing its extension into more immanent terrain.