Capability approach
A welfare framework judging well-being by what people are actually able to do and be, not by income or resources alone.
What it means
The capability approach evaluates individual advantage in terms of capabilities (the real freedoms or opportunities a person has) and functionings (the beings and doings they actually achieve), rather than by resources, utility, or preference satisfaction. Its central move is to ask what a person is genuinely able to do given their circumstances — two people with the same income can have very different real freedoms because of health, disability, or social barriers. Though developed as a theory of justice and development economics, it bears directly on behavior policy by reframing the goal of intervention as expanding agency and real options, not merely steering choices. It is deliberately under-specified about which capabilities matter most, which is both a flexibility and a critique. It matters because it offers behavioral practitioners an ethical yardstick — does this intervention enlarge people's real freedom, or just their compliance?
Conversion factors
The engine of the approach is that resources are only inputs; what matters is a person's ability to convert them into functionings. Sen distinguishes three conversion factors: personal (metabolism, literacy, impairment), social (norms, discrimination, public institutions) and environmental (climate, infrastructure, distance). A bicycle yields mobility only to someone able to ride it, on passable roads, in a society that lets them. The approach also sharpens two distinctions: freedom versus achievement (having an option versus taking it), and well-being versus agency (living well versus pursuing goals one has reason to value, even against one's own welfare).
The list problem
The approach's most persistent internal fault line is whether to name the capabilities that count. Sen refused, holding that the selection and weighting of capabilities is itself a democratic, context-dependent exercise no theorist should settle in advance. Nussbaum disagreed, arguing a normative theory owes people a concrete threshold, and proposed ten central capabilities — life, bodily health, bodily integrity, senses and thought, emotions, practical reason, affiliation, other species, play, and control over one's environment — that governments should secure for all. The tension is unresolved: Sen buys flexibility at the cost of guidance; Nussbaum buys guidance at the cost of a universalism others can contest.
From theory to measurement
Because it treats well-being as plural, the approach pushed measurement away from single-number, income-based metrics. Its most visible offspring is the UN Human Development Index, which Sen helped shape, combining income with life expectancy and education. More faithful to the framework is the global Multidimensional Poverty Index, built on the Alkire-Foster method, which counts a person as poor by the overlapping deprivations they actually experience across health, education and living standards rather than by a dollar line. Both are compromises — they measure functionings, which are observable, as proxies for capabilities, which are not — but they put the core intuition into official statistics.
Where it meets behavioral policy
For a practitioner the approach is a standing challenge to nudging. A default that raises pension enrolment improves an outcome, but the capability question is whether it also widens a person's real command over their options or merely their compliance with the designer's aim. This maps onto the individual-frame versus system-frame debate: nudges usually act on the i-frame, while capabilities are often blocked at the s-frame — no accessible station, no broadband, no spare hour. A small capabilitarian literature now argues the two can be combined, using behavioral insight to remove the frictions that stop people converting resources into functionings rather than to steer choices toward a fixed answer.
Limits and critiques
The recurring objection is operational: with no fixed list, and capabilities defined as unrealized freedoms, the framework is hard to measure and easy to fill with the evaluator's own priorities. A second charge is ethical individualism — it scores each person's freedoms and can under-weight the collective and relational goods, families and communities, through which lives are lived. A third is practical: once agencies adopt it, capabilities can harden into another checklist of required functionings, quietly reintroducing the paternalism it set out to escape. None of these sink it, but they explain why it endures more as an ethical compass than as a settled measurement recipe.
Examples
A transport subsidy expands capability only if people can actually use it — for someone with a disability and no accessible station, the resource exists but the real freedom to travel does not.
A company gives every employee free gym membership, but the night-shift staff clock off at midnight and the gym shuts at ten. Equal resource, unequal freedom to actually use it.
Handing every pupil a laptop expands capability only where there is broadband, a quiet corner to work in, and someone to fix it — otherwise the resource converts into nothing.
A clinic offers free screening, but appointments run only on weekday mornings, so a single parent on an hourly wage holds the entitlement yet has no real freedom to attend.
A bank waives all fees on savings accounts, but a cash-paid worker with no ID and no branch nearby cannot open one; the offer is universal, the capability is not.
First described in Amartya Sen (1980s); developed by Martha Nussbaum.
Key references
- Garces-Velastegui, P. (2024). A capabilitarian behavioral economics: what behavioral economics can learn from the capability approach. International Review of Economics, 71(3), 667-690. doi.org/10.1007/s12232-024-00457-8
- Garces-Velastegui, P. (2023). Towards a behavioural capability approach: the contribution of behavioural economics to Amartya Sen's framework. International Review of Economics, 70(1), 101-120. doi.org/10.1007/s12232-023-00411-0
- Robeyns, I. (2017). Wellbeing, Freedom and Social Justice: The Capability Approach Re-Examined. Cambridge: Open Book Publishers. doi.org/10.11647/OBP.0130
- Nussbaum, M. C. (2011). Creating Capabilities: The Human Development Approach. Cambridge, MA: Belknap Press of Harvard University Press. www.hup.harvard.edu/books/9780674072350
- Robeyns, I. (2005). The Capability Approach: a theoretical survey. Journal of Human Development, 6(1), 93-117. doi.org/10.1080/146498805200034266
- Sen, A. (1980). Equality of What? In S. McMurrin (Ed.), The Tanner Lectures on Human Values (Vol. 1, pp. 197-220). Cambridge: Cambridge University Press. tannerlectures.org/lectures/equality-of-what/