 This formal aspect of the modal analysis has been prominent in the philosophical and linguistic literature because the standard semantics for ability ascriptions is an explicitly modal one. This is the view developed in a series of papers by Angelika Kratzer (Kratzer 2012). Kratzer treats expressions such as ‘S can A’ and ‘S is able to A’ as possibility claims. That is, ‘S is able to A’ is true just in case there is a possible world w meeting certain conditions at which S does A. The conditions are that (i) w be accessible given some contextually-specified set of facts (the modal base) and (ii) that w be at least as good, according to a contextually-specified ranking of worlds (the ordering source), as any other accessible world. The Kratzer semantics is thus an instance of the modal analysis on its semantic formulation: