As an introductory note to the substance of this paper, I should like to start by not apologizing for begging in my own favour the major problems involved in interpreting historical texts in political theory. It will be obvious from the body of the paper that James Mill and his son appear here to illustrate a wide thesis concerning two contrasting images of the nature of politics, images that are important in their own right, and especially so in the context of recent Anglo-American political science. It might be complained that thus to use them involves riding roughshod over historical accuracy, or - to change the metaphor - that I have thrust my protagonists into a Procrustean bed of my own devising, ignoring the eccentricities, the quirks of doctrine that any biographer has to stress. A real defence against such a charge can only lie in the insights hopefully provided by the paper itself; but I should at once state that if I must plead guilty, I remain unrepentant. For my purpose is not to re-create exactly what James Mill or J. S. Mill thought he was saying, but rather to elucidate with all the assistance that hindsight can give us what kind of case each of them was making.