In 1822, James Mackintosh found much that was admirable in Mill’s essays on government and education. However, Mackintosh protested, they were founded on an erroneous method (Mackintosh to Napier, 1822). Less than a decade later, Macaulay devastatingly drew out the implications of that method for Mill’s “utilitarian logic and politics.” In  reviewing the quarrel between Mill and Macaulay today, the modern reader may well experience a sense of déjà vu, not because the question of parliamentary reform remains relevant and timely, but because the epistemological and methodological questions raised by this debate are with us still. What is the nature of political knowledge, and how is it to be obtained? What sort of “science” can “political science” aspire to be? What is the connection between political theory and the practice of politics? Mill’s answers rather resemble those of modern “rational choice” theorists, and Macaulay’s those of their empirically minded critics. After all, Mill maintains that any scientific theory worthy of the name must proceed from a finite set of assumptions about human nature, with the self-interest axiom at their center. From these one can deduce conclusions about the ways in which rational political actors will (or at any rate ought to) behave. Macaulay, by contrast, claims that people act for all sorts of reasons, including—but by no means limited to—considerations of self-interest.