and in terms of the idea of a knowledge by which such entities are cognized. The kind of Being which belongs to entities within-the-world is something which they themselves might have been permitted to present; but Descartes does not let them do so.1 Instead he prescribes for the world its 'real' Being, as it were, on the basis of an idea of Being whose source has not been unveiled and which has not been demonstrated in its own right—an idea in which Being is equated with constant presence-at-hand. Thus his ontology of the world is not primarily determined by his leaning towards mathematics, a science which he chances to esteem very highly, but rather by his ontological orientation in principle towards Being as constant presence-at-hand, which mathematical knowledge is exceptionally well suited to grasp. In this way Descartes explicitly switches over philosophically from the development of traditional ontology to modern mathematical physics and its transcendental foundations.
The problem of how to get appropriate access to entities within-the-world is one which Descartes feels no need to raise. Under the unbroken ascendance of the traditional ontology, the way to get a genuine grasp of what really is [des eigentlichen Seienden] has been decided in advance: it lies in νοεῖν—'beholding' in the widest sense [der "Anschauung" im weitesten Sinne]; διανοεῖν or 'thinking' is just a more fully achieved form of νοεῖν and is founded upon it. Sensatio (αἴσθησις), as opposed to intellectio, still remains possible as a way of access to entities by a beholding which is perceptual in character; but Descartes presents his 'critique' of it because he is oriented ontologically by these principles.
Descartes knows very well that entities do not proximally show themselves in their real Being. What is 'proximally' given is this waxen Thing which is coloured, flavoured, hard, and cold in definite ways, and which gives off its own special sound when struck. But this is not of any importance ontologically, nor, in general, is anything which is given through the senses. " Satis erit, si advertamus sensuum perceptiones non referri, nisi ad istam corporis humani cum mente coniunctionem, et nobis quidem ordinarie exhibere, quid ad illam externa corpora prodesse possint aut nocere ..."xviii The senses do not enable us to cognize any entity in its Being; they merely serve to announce the ways in which 'external' Things within-the-world are useful or harmful for human creatures encumbered with bodies. " . . . non . . . nos docere,  qualia <corpora> in seipsis existant ";xix they tell us nothing about entities in their Being. " Quod agentes, percipiemus naturam materiae, sive corporis in universum spectati, non consistere in eo quod sit res dura, vel ponderosa, vel colorata,
1 'Descartes lässt sich nicht die Seinsart des innerweltlichen Seienden von diesem vorgeben ...'