 The two sides identified by Berlin disagree over which of two different concepts best captures the political ideal of ‘liberty’. Does this fact not denote the presence of some more basic agreement between the two sides? How, after all, could they see their disagreement as one about the nature of liberty if they did not think of themselves as in some sense talking about the same thing? In an influential article, the American legal philosopher Gerald MacCallum (1967) put forward the following answer: there is in fact only one basic concept of freedom, on which both sides in the debate converge. What the so-called negative and positive theorists disagree about is how this single concept of freedom should be interpreted. Indeed, in MacCallum’s view, there are a great many different possible interpretations of freedom, and it is only Berlin’s artificial dichotomy that has led us to think in terms of there being two.