When developing a capability theory it is often necessary to specify what additional descriptive, normative, metaphysical, and/or meta-theoretical commitments are made. As mentioned, the purpose of one’s theory might determine some of the commitments that the theory must adhere to, however in other cases this is not necessarily so. For example, while a capability theory of distributive justice - more on which in section 4 - is committed to conceptualizing justice primarily in terms of the fair distribution of capabilities and functionings, it is an open question whether the distribution of other normative concerns, such as utility, happiness, or resources, should play a secondary role. Likewise, the choice of distributive principle is also open and one may develop sufficientarian, strict egalitarian, or prioritarian theories of justice, all of which are committed to the distribution of capabilities and functionings, while the notion of responsibility that is employed may rely on different descriptive theories of human beings as either fully or only partially rational beings. A capability theory of justice may also include metaphysical commitments that extend rights and responsibilities to non-human animals and entities.