This holds true—and by no means least—for that understanding which is rooted in Dasein's ownmost Being, and for the possibility of developing it—namely, for ontological understanding.
When tradition thus becomes master, it does so in such a way that what it 'transmits' is made so inaccessible, proximally and for the most part, that it rather becomes concealed. Tradition takes what has come down to us and delivers it over to self-evidence; it blocks our access to those primordial 'sources' from which the categories and concepts handed down to us have been in part quite genuinely drawn.1 Indeed it makes us forget that they have had such an origin, and makes us suppose that the necessity of going back to these sources is something which we need not even understand. Dasein has had its historicality so thoroughly uprooted by tradition that it confines its interest to the multiformity of possible types, directions, and standpoints of philosophical activity in the most exotic and alien of cultures; and by this very interest it seeks to veil the fact that it has no ground of its own to stand on. Consequently, despite all its historiological interests and all its zeal for an Interpretation which is philologically 'objective' ["sachliche"], Dasein no longer understands the most elementary conditions which would alone enable it to go back to the past in a positive manner and make it productively its own.
We have shown at the outset (Section I) not only that the question of the meaning of Being is one that has not been attended to and one that has been inadequately formulated, but that it has become quite forgotten in spite of all our interest in 'metaphysics'. Greek ontology and its history—which, in their numerous filiations and distortions, determine the conceptual character of philosophy even today-prove that when Dasein  understands either itself or Being in general, it does so in terms of the 'world', and that the ontology which has thus arisen has deteriorated [verfällt] to a tradition in which it gets reduced to something self-evident—merely material for reworking, as it was for Hegel. In the Middle Ages this uprooted Greek ontology became a fixed body of doctrine. Its systematics, however, is by no means a mere joining together of traditional pieces into a single edifice. Though its basic conceptions of Being have been taken over dogmatically from the Greeks, a great deal of unpretentious work has been carried on further within these limits. With the peculiar character which the Scholastics gave it, Greek ontology has, in its essentials, traveled the path that leads through the Disputationes metaphysicae of Suarez to the 'metaphysics' and transcendental philosophy of modern times, determining even the foundations and the aims of Hegel's 'logic'.
1 In this passage Heidegger juxtaposes a number of words beginning with the prefix 'über-'; 'übergibt' ('transmits'); 'überantwortet' ('delivers over'); 'das Überkommene' ('what has come down to us'); 'überlieferten' ('handed down to us').