The essay agues that there is little scope for ideal theory in political philosophy, even under Rawls’s conception of its aims. It begins by identifying features of a standard example of ideal theory in physics — the ideal gas law, PV=NRT and draws attention to the lack of these features in Rawls’s derivation of the principles of justice from the original position. A. John Simmons’s defense of ideal theory against criticisms of Amartya Sen is examined, as are further criticisms of both by David Schmidtz. The essay goes on to develop a conception of the domain of social relations to be characterized by justice that suggests that as a moving target it makes ideal theory otiose. Examination of Rawls’s later views substantiate the conclusion that ideal theory as propounded in A Theory of Justice is a mistaken starting point in the enterprise of political philosophy. Differences between the domains of ideal theory in mathematics, physics, and economics on the one hand, and political philosophy on the other, reinforce this conclusion.