In our exposition of the problem of worldhood, we suggested the importance of obtaining proper access to this phenomenon. So in criticizing the Cartesian point of departure, we must ask which kind of Being that belongs to Dasein we should fix upon as giving us an appropriate way of acess to those entities with whose Being as extensio Descartes equates the Being of the ‘world’. The only genuine access to them lies in knowing [Erkennen], intellectio, in the sense of the kind of knowledge [Erkenntnis] we get in mathematics and physics. Mathematical knowledge is regarded by Descartes as the one manner of apprehending entities which can always give assurance that their Being has been securely grasped. […] 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.

Martin Heidegger, Being and Time, translated by John Macquarrie and Edward Robinson