William Pitt's 1785 proposal for a free trade area between Britain and Ireland attempted to use free trade as a mechanism of imperial integration. It was a response to the agitation for political reform in Ireland and followed the attainment of legislative independence in 1782. The proposal aimed at coordinating economic and fiscal policy between the kingdoms without imposing explicit political controls. This article establishes that the measure failed because of the lack of consensus around the idea of free trade. Three contrasting ideas of free trade became apparent in the debates around the propositions of 1785: imperial or neomercantilist free trade, Smithean free trade, and national or neo-Machiavellian free trade. Imperial free trade was critical of monopolies but sought to organize trade to the benefit of the imperial metropole; Smithean free trade saw open markets as a discipline that assured efficiency but required imperial institutional frameworks, legally secured, to function. Neo-Machiavellian free trade asserted the right of every political community to organize its trade according to its interests. The article establishes the genealogy of these three positions in pamphlet debates and political correspondence in Britain and Ireland from 1689 to 1785. It argues that majority political opinion in Ireland, with exceptions, understood free trade in a neo-Machiavellian sense, while Pitt was committed to a Smithean ideal. The propositions collapsed because these internal tensions became more evident under the pressure of criticism. Liberal political economy did not of itself offer a route to a British exceptionality that finessed the tensions inherent in empire.