Mill's System of Logic (1843) indicates that the definition of ‘nationality’ he offered in Considerations on Representative Government (1861) is not a throwaway comment but a carefully considered causal hypothesis tailored to his politico-ethological research programme. This matters because Lord Acton's critique of Mill's claim that free institutions are almost impossible in multinational states ignored the definition, thereby obscuring subsequent scholars' vision of the conceptual dimension of this famous dispute. Although Mill struggled in his politico-ethological endeavour, he was sufficiently confident (...) to judge that, if nationalities seek self-determination through exclusive control of the state, liberal democratic institutions would be unlikely to emerge in multinational states, let alone survive and prosper. Since Acton's critique presupposed an undemocratic conception of free institutions and a far weaker notion of national self-determination, it failed to contradict that judgement. Indeed, once their conceptual disagreements are clarified, Acton's empirical analysis can be seen to support it. (shrink)