Measurements are procedures that allow different observers to form an agreement about states of the world. To be effective, measurements require the correct metric and the appropriate measuring tool. You cannot measure weight with a ruler or distance in kilograms. If you infer the weight of a people by measuring their height, the results will appear plausible in some cases but would be fundamentally flawed in many other cases. But what is the metric of distributive justice? If we discuss whether a distribution is fair, we first need to agree upon the appropriate metric: A distribution of what?

One of the significant philosophical contributions of John Rawls in A Theory of Justice (1971) was his decision to move away from metrics of justice that are based on subjective metrics of well-being, such as overall happiness, to objective metrics. Both subjective and objective metrics require taking a normative stand about the meaning of well-being. Subjective metrics (asking “Are you happy?”) delegate the normative evaluation de facto to the person being measured. Rawls's philosophical shift was to frontload the normative commitments that underlie measurement. He did so by having the theory of justice focused on the distribution of an agreed-upon set of primary goods that serve as resources that enable people to pursue their different paths for happiness. This allowed him to separate the normative commitments related to measurement from those related to distribution.

Proponents of the capability approach, which was developed by Amartya Sen, agree with Rawls's frontloading of the normative commitments related to measurement but disagree with the actual commitments that underlie the choice of primary goods. For them, measuring justice by the distribution of primary goods is akin to measuring height with a scale in kilograms. The outcomes sometimes appear to make sense, but for the most part, it is not the right metric and not the right tool. Well-being cannot be measured by having equal means to pursue a good life. The relevant metric is the degree of freedom to achieve the functioning that one chooses. It is to be measured by the set of capabilities that are needed to achieve this functioning, a set that is different for each individual (one needs health care to run a marathon, another to write a poem). Thus, to take an example that is often invoked in this context, a man and a woman can have different prospects for achieving meaningful careers despite having equal wealth. They have similar resources, but they do not have the same capabilities to translate these resources into the functioning of their choice.

Measuring Justice is an edited volume containing 11 original essays by leading political philosophers that explore the contours of the debate between advocates of a metric of resources and advocates of a metric of capabilities. It begins with a short introduction by the volume's editors, Harry Brighouse and Ingrid Robeyns, which offers a useful summary of the history of the debate. The theoretical aspects of the debate are explored in the first part, with essays by Thomas Pogge, Erin Kelly, Elizabeth Anderson, and Richard J. Arneson. This part is followed by five essays that examine “applications” of the debate for the areas of health (Norman Daniels), disability (Lorella Terzi), children (Colin M. Macleod), education (Brighouse and Elaine Unterhalter), and gender (Robeyns). The volume ends with a very helpful summary by Amartya Sen that reviews the broader context of the debate and replies to some of the arguments.

This volume is required reading for anyone who has a stake in the topic. It presents the key arguments of the contemporary debate and brings together some of the major contributors to it (with the notable exception of Martha Nussbaum). In this review, I choose not to engage directly with the complex arguments presented there. Instead, I want to follow what I take to be the spirit of Perspectives and discuss the possible reach of this volume beyond political theory and into the wider community of political science.

On the one hand, it is not difficult to see why such a reach may be limited. First, the distinction between resources and capabilities takes place at the level of abstract theorizing, and it does not have a one-on-one relationship with any specific policies or specific empirical measurements. Rawls was not against special policies for people with disabilities. He argued only that such a policy should be worked out at a legislative stage and not as part of the agreement in an original position. In a similar way, advocates of capabilities do not think that justice requires setting standards for all possible capabilities but only for a small number of crucial ones. Each approach will provide different reasoning to justify policies, a point that I will return to momentarily, but it is hard to pinpoint a policy that only one approach will necessarily endorse and not the other. It is true that the capabilities approach inspired development economists to come up with the Human Development Index (HDI), which acknowledges a plurality of development goals as part of a measure of welfare (p. 2). But, again, there is no particular reason why a thoughtful resourcist should not endorse this or another complex measure of human development. In this context, Pogge is right in objecting to the suggestion that resourcists necessarily endorse simplistic measures, such as average income or GNP per capita (p. 19).

I also think that the volume might be unfriendly to the nonspecialist audience in that it frames the discussion as one of deciding which approach is right. However, as the debates in Measuring Justice unfold, it becomes clear that the choice of resources or capabilities is a relatively technical part of other more important theoretical choices (Sen himself makes a similar point in his essay, and he stresses that the debate is “in a limited arena in a specific domain” [p. 242]). The various chapters, and particularly the ones on “applications,” go back and forth between high theory and a careful analysis of the specific social and policy arena in which the theory can be applied. I think that these discussions are much more interesting and far richer not when they try to decide which approach is better but when they explore how each approach can provide frameworks about the meaning of well-being in, and arguments about, their distributive implications. This is the first context in which the volume is of relevance to political scientists: It provides a rich analysis of arguments that can be deployed in debates about distributions of resources and the social conditions that make these arguments plausible. The analysis of such arguments can play a role in the study of relations of power and in social criticism. Arguments based on equality of resources can disguise patriarchal power and gender inequality (p. 218), and those based on equality of capabilities can serve as a host for paternalist domination (p. 120). Unmasking these power relations requires a complex understanding of the meaning of equality and well-being.

Furthermore, political scientists should read the volume to reflect on the ways in which the questions of “why we measure” and “what we measure” are related. To be sure, the claim that social science measurements can perform speech acts and have normative implications should not come as news to political scientists. Nonetheless, the fact that the contributors share similar ideological sensibilities and the sophistication of the arguments provide an opportunity to explore the normative complexity of measurements in the social sciences. The volume also allows an exploration of the relationship between “what we measure” and” how we measure” in discussing the differences between objective and subjective measures of well-being and in discussing the degrees of publicity of certain measures.

I believe that this edited volume can be a wonderful (albeit unconventional) addition to a reading list in an advanced-level course on research methods. Elizabeth Anderson's essay is particularly suitable for such a purpose.