Mulhall: a natureza da investigação heideggeriana
"[...] philosophy has no authority to judge the validity of specific scientific theories. But any such theory is constructed and tested in ways which presuppose the validity of certain assumptions about the domain under investigation, assumptions that it can consequently neither justify nor undermine, and which therefore require a very different type of examination. The scientist may well be the best exponent of the practices of inductive reasoning as applied to the realm of nature; but if questions are raised about the precise structure of inductive reasoning and its ultimate justification as a mode of discovering truth, then the abilities of the philosopher come into play.
This is a familiar view of the role of philosophical enquiry in the Western philosophical tradition, particularly since the time of Descartes — at least if we judge by the importance it has assigned to the twin ontological tasks of specifying the essential differences between the various types of entity that human beings encounter, and the essential preconditions of our capacity to comprehend them. To learn about that tradition is to learn, for example, that Descartes’ view of material objects — as entities whose essence lies in being extended — was contested by Berkeley’s claim that it lies in their being perceived, whereas his view that the essence of the self is grounded in the power of thought was contested by Hume’s claim that its only ground is the bundling together of impressions and ideas. Kant then attempts to unearth that which conditions the possibility of our experiencing ourselves as subjects inhabiting a world of objects. Alternatively, we might study the specific conceptual presuppositions of aesthetic judgements about entities as opposed to scientific hypotheses about them, or interrogate the distinctive presuppositions of the human sciences — the study of social and cultural structures and artefacts, and the guiding assumptions of those who investigate them as historians rather than as literary critics or sociologists.
 In a terminology Heidegger sometimes employs in other texts, such ontological enquiries broadly focus on the what-being of entities  — their particular way or mode of being. Their concern is with what determines an entity as the specific type of entity it is, with that which distinguishes it from entities of a different type, and grounds both our everyday dealings with such entities and our more structured and explicit ontic investigations of the domain they occupy. Such a concern with what-being is to be contrasted with a concern with that-being. ‘That-being’ signifies the fact that some given thing is or exists,  and an ontological enquiry into that-being must concern itself with that which determines an entity of a specific type as an existent being -something equally fundamental both to our everyday dealings with it and to our ontic investigations of it, since neither would be possible if the entity concerned did not exist. A general contrast of this kind between what-being and that-being is thus internal to what Heidegger means by the Being of beings; it is a basic articulation of Being, something which no properly ontological enquiry can afford to overlook. And indeed, the Western philosophical tradition since Plato has not overlooked it; but the way in which that tradition has/tended to approach the matter has, for Heidegger, been multiply misleading."
Mulhall, Stephen. "Heidegger and Being and time", p.4-7