You have every right to get angry

In this rich and densely argued book, Matthew Kramer defends an austere, negative account of freedom - "a theory", as he puts it, "that construes liberty as a state of unpreventedness".

The twin pillars of his account are the F postulate: "A person is free to ø if, and only if, he is able to ø." And the U postulate: "A person is unfree to ø if, and only if, both of the following conditions obtain: (1) He would be able to ø in the absence of the second of these conditions; (2) Irrespective of whether he actually endeavours to ø, he is directly or indirectly prevented from ø-ing by some action(s) or some disposition(s)-to-perform-some-action(s) on the part of some other person(s)."

Although much of the book focuses on defending this account of negative liberty, the arguments are driven by the central aim of the book, to show that the overall liberty of each person can (in principle) be measured.

The second chapter begins with a certain amount of useful clarification and ground-clearing. In particular, Kramer distinguishes his account from two other versions of negative liberty. In one, what matters is whether a person is able to do what he or she wants. In the other, what matters is whether a person is permitted (or not) by legal and moral norms or rules from performing certain actions. Kramer's theory, by contrast, is strictly desire-independent and non-normative. These distinctions appear, in some part, because they play a role in identifying mistakes in Quentin Skinner's understanding of negative liberty, and his more occasional errors in his readings of Hobbes. The second half of the chapter concerns itself more directly with Skinner's (and Philip Pettit's) espousal of a civic-republican understanding of liberty. Kramer's strategy is to show that, at least as a conception of freedom (as against as a general political stance), civic-republicanism adds nothing to the account of negative freedom.

The third and fourth chapters focus on particular freedoms and unfreedoms. Kramer considers over what range of things freedom can pertain. Rejecting the argument that only actions can be free or unfree, he argues for a more expansive applicability of the notion of freedom - so that, for example, one can be free to become angry. He also asks whether particular freedoms come in degrees (and argues that they do not); in what ways freedoms depend on counter-factuals (potential events that do not, but that could have, occurred); and argues that when thinking about the value of freedom, we ought to distinguish between the value of performing some action (X), the value of the freedom specifically to do X, and the value of the freedom to do X as a sheer freedom.

Kramer takes up some of the problems that arise from endorsing the U postulate in chapter four. Specifically, it is part of the U postulate that we determine the presence or absence of unfreedom (as against mere incapacity or inability) by identifying constraints due to other people and those due to nature or the agent's own conduct. Much of chapter four, then, is concerned with the criteria that determine where the causal responsibility for freedom-impairing constraints lies.

Chapter five offers the means by which freedom can be measured. It focuses in part on how freedoms and unfreedoms can be individuated so they can be fed into the formula that determines overall freedom. The fact that a book on freedom can end in a mathematical formula will no doubt anger and perplex some readers. However, they should still be impressed by the quality of the arguments and ought to pause to reflect how often principles of justice enjoin us to distribute (to maximise or equalise) freedom.

I am conscious of offering little more than a slightly annotated table of contents. In part, this is a reaction to the impossibility of offering an overall account, let alone evaluation, of a book packed with arguments.

What can be said is that this book makes a significant contribution to the literature on freedom.

Some specialists and non-specialists alike will baulk at the extremely thin and austere account that Kramer offers. However, even those who profoundly disagree will often be stopped in their tracks by the relentlessness and quality of Kramer's work.

Matt Matravers is senior lecturer in political philosophy, York University.