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:ἰδεῖν), 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)