The capability approach is generally conceived as a flexible and multi-purpose framework, rather than a precise theory of well-being (Qizilbash 2008; Robeyns 2005, 94-96; Sen 1992; 2009). This open-ended and underspecified nature partly explains why the term ‘capability approach’ was chosen and is now used in the philosophical literature rather than, say, ‘capability theory’. The terms ‘capability approach’ and ‘capabilities approach’ are both used in the literature to refer to the same thing, though the latter is often considered to refer more specifically to Nussbaum’s partial theory of justice. Some philosophers have started to use the term ‘capabilitarianism’ (Robeyns 2016; Nielsen and Axelsen 2017). The proliferation of literature on the capability approach has engendered a discussion about how to exactly define and understand it.