  The question which institutions count as authoritative in the system is to be settled in the first instance by other norms constituted by authoritative directive that count as more fundamental. But this kind of explanation can only go so far. To avoid regress, the question must be settled ultimately by some factor other than an authoritatively created norm. A prominent suggestion is that the factor that ultimately explains legal authority is the settled official practice of recognition of the action of certain agents or institutions as a source of norms (a practice that may be considered itself as constituting a customary norm that is tacitly endorsed in and regulates official practice and from which legal institutions ultimately derive their authority to create valid norms; Hart 1994).