With Plato  , this early Greek conception of φύσις  -ἀλήθεια   [physis-aletheia], sc. truth conceived as non-concealment [Unverborgenheit  ], undergoes a transformation, for, although on the one hand   the Ideas retain the original sense of ἀ-λήθεια [a-letheia], insofar as they are conceived fundamentally as a source of light [Licht  ] by reason of which, through participation [methexis  ], the “beings” of experience shine forth, nevertheless the Ideas become at the same time something-to-be-seen (εἶδος:ἰδεῖ  ν), and truth [Wahrheit  ] comes gradually to mean the proper viewing of the Ideas, the conformity (ὀρθότης [orthotes  ]) between the being that views and the Ideas (conceived as beings) that are viewed. Here the Ideas are transformed from a source of light into that-which-is-viewed. In other words, Being [Sein  ] is reduced to a being [Seiende  ]. The confusion will mark the entire subsequent history of metaphysics [Metaphysik  ]. Token of the confusion will be the domination henceforth of the conception of truth as conformity and a disregard of the original sense of truth as non-concealment. Since truth-as-non-concealment is what Heidegger understands by Being, it is easy to see in what sense he understands metaphysics as the perennial forgetfulness of Being [Seinsvergessenheit  ]. [RHPT:17]