 An influential paper by Martin Davies and Lloyd Humberstone (1980) brought the formal tools developed in 2D modal logic to bear on philosophical puzzles about modality. Following Gareth Evans (1979), Davies and Humberstone suggest that there are two notions of metaphysical necessity involved in ordinary modal thinking: deep and superficial necessity. They argue that the two logical operators, ‘\(\mathcal{F}\mathcal{A}\)’ and ‘\(\Box\)’, respectively, provide a clear formal elucidation of these two notions.