  As this suggests, Heidegger subscribes to a doctrine of ontological historicity (refining a view first developed by Hegel). Put simply, Heidegger thinks that humanity’s fundamental experience of reality changes over time (sometimes dramatically), and he suggests that the work of art helps explain the basic mechanism of this historical transformation of  intelligibility.[5] Because great art works inconspicuously to establish, maintain, and transform humanity’s historically-variable sense of what is and what matters, Heidegger emphasizes that “art is the becoming and happening of truth” (PLT 71/GA5 59). Put simply, great artworks help establish the implicit ontology and ethics through which an historical community understands itself and its  world.[6] In keeping with this (initially strange) doctrine of ontological historicity, Heidegger understands “truth” ontologically as the historically-dynamic disclosure of intelligibility in time. As we will see in section 3, this historical unfolding of truth takes place—to use Heidegger’s preferred philosophical terms of art—as an “a-lêtheiac” struggle to “dis-close” or “un-conceal” (a-lêtheia) that which conceals (lêthe) itself, an “essential strife” between two interconnected dimensions of intelligibility (revealing and concealing) which Heidegger calls “world” and “earth” in his most famous work on art.