Onora O'Neill...argues that people (and perhaps some other creatures) who dwell together in the ways I have discussed stand in relations where principles of justice ought to apply. An agent stands in relations of justice with all those others whose actions that agent assumes in the background of his or her own actions. In going about our own business we assume that many others will or will not do things whose institutional and causal consequences can affect our lives and actions, and we likewise implicitly assume our actions as institutionally and causally connected to the lives and actions of others. On O'Neill's account, people have obligations justice to others insofar as and on account of this fact that they assume the specific agency of others as premisses for their own action.
The citation to O'Neill is Onora O'Neill, Toward Justice and Virtue (Cambridge: Cambridge UP, 1996), ch. 3.