Full Idea
Capability is an aspect of freedom, concentrating in particular on substantive opportunities.
Gist of Idea
Capabilities are part of freedom, involving real opportunities
Source
Amartya Sen (The Idea of Justice [2009], 13 'Well-being')
Book Reference
Sen, Amartya: 'The Idea of Justice' [Penguin 2010], p.287
A Reaction
This is the 'capabilities approach' of Sen and Nussbaum. The key word is 'substantive' (as opposed to theoretical). We are all free to become astronauts, but....