Ignorance, Incompetence and the Concept of Liberty*

W HAT is liberty, and can it be measured?Much attention has been deservedly lavished on these critical political questions, and the result has been some hard-earned philosophical progress.1 In this article I hope to inch us a little further.I shall argue that the only way to have a liberty metric is to adopt an account of liberty with specific and controversial features.In particular, I shall argue that we can make sense of the idea of a quantity of liberty only if we are willing to count certain purely agential constraints, such as ignorance and physical incompetence, as obstacles to liberty in general.This spells trouble for traditional 'negative' accounts, against which I argue directly.My aim is to establish the following somewhat surprising claim: that if a political theory is to contain a principle regarding the protection, maximisation or equalisation of some liberty, it must concern itself-on pain of conceptual incoherence-with the positive preconditions (in addition to the negative preconditions) of that liberty's effective exercise.Many political theorists have denied that political theories ought to contain any principles that make essential reference to quantities or extents of liberty.If correct, this would render my conditional claim relatively uninteresting.I shall therefore begin by arguing that such theorists are mistaken. I. A DISTINCTIONConsider the following two liberty claims:(1) A is at liberty to go to the park (2) A has liberty of movement *Thanks to Jennifer Whiting and to Arthur Ripstein for help in developing the ideas presented in this paper; thanks also to Keith Dowding for providing extensive and valuable comments on an earlier draft.