Everyone who is acquainted with the middle ages sees that Descartes is ‘dependent’ upon medieval scholasticism and employs its terminology. But with this ‘discovery’ nothing is achieved philosophically as long as it remains obscure to what a profound extent the medieval ontology has influenced the way in which posterity has determined or failed to determine the ontological character of the res cogitans. The full extent of this cannot be estimated until both the meaning and the limitations of the ancient ontology have been exhibited in terms of an orientation directed towards the question of Being. In other words, in our process of destruction we find ourselves faced with the task of Interpreting the basis of the ancient ontology in the light of the problematic of Temporality. When this is done, it will be manifest that the ancient way of interpreting the Being of entities is oriented towards the ‘world’ or ‘Nature’ in the widest sense, and that it is indeed in terms of ‘time’ that its understanding of Being is obtained. The outward evidence for this (though of course it is merely outward evidence) is the treatment of the meaning of Being as parousia or OUSIA, which signifies, in ontologico-Temporal terms, ‘presence’ [“Anwesenheit”]. Entities are grasped in their Being as ‘presence’; this means that they are understood with regard to a definite mode of time – the ‘Present’ BTMR §6
The problematic of Greek ontology, like that of any other, must take its clues from Dasein itself. In both ordinary and philosophical usage, Dasein, man’s Being, is ‘defined’ as the zoon logon echon – as that living thing whose Being is essentially determined by the potentiality for discourse. legein is the clue for arriving at those structures of Being which belong to the entities we encounter in addressing ourselves to anything or speaking about it [im Ansprechen und Besprechen]. (Cf. Section 7 b.) This is why the ancient ontology as developed by Plato turns into ‘dialectic’. As the ontological clue gets progressively worked out – namely, in the ‘hermeneutic’ of the logos – it becomes increasingly possible to grasp the problem of Being in a more radical fashion. The ‘dialectic’, which has been a genuine philosophical embarrassment, becomes superfluous. That is why Aristotle ‘no longer has any understanding’ of it, for he has put it on a more radical footing and raised it to a new level [aufhob]. legein itself – or rather noein, that simple awareness of something present-at-hand in its sheer presence-at-hand, which Parmenides had already taken to guide him in his own interpretation of Being – has the Temporal structure of a pure ‘making-present’ of something. Those entities which show themselves in this and for it, and which are understood as entities in the most authentic sense, thus get interpreted with regard to the Present; that is, they are conceived as presence (OUSIA). BTMR §6
Descartes distinguishes the ‘ego cogito’ from the ‘res corporea’. This distinction will thereafter be determinative ontologically for the distinction between ‘Nature’ and ‘spirit’. No matter with how many variations ‘of content the opposition between ‘Nature’ and ‘spirit’ may get set up ontically, its ontological foundations, and indeed the very poles of this opposition, remain unclarified; this unclarity has its proximate [nächste] roots in Descartes’ distinction. What kind of understanding of Being does he have when he defines the Being of these entities? The term for the Being of an entity that is in itself, is “substantia”. Sometimes this expression means the Being of an entity as substance, substantiality; at other times it means the entity itself, a substance. That “substantia” is used in these two ways is not accidental; this already holds for the ancient conception of OUSIA. [SZ:90] BTMR §19
This question has today been forgotten. Even though in our time we deem it progressive to give our approval to ‘metaphysics’ again, it is held that we have been exempted from the exertions of a newly rekindled gigantomachia peri tes OUSIAS. Yet the question we are touching upon is not just any question. It is one which provided a stimulus for the researches of Plato and Aristotle, only to subside from then on as a theme for actual investigation. What these two men achieved was to persist through many alterations and ‘retouchings’ down to the ‘logic’ of Hegel. And what they wrested with the utmost intellectual effort from the phenomena, fragmentary and incipient though it was, has long since become trivialized. [SZ:2] BTMR §1