Basic-concepts or ground-concepts involves the readiness to reach the ground and not let it go again. For Heidegger, to grasp the ground means to grasp Being; and this in turn means grasping the original Greek inception. To this purpose, Heidegger presents and elaborates the ontological distinction between Being and beings; probably with more details and at length than in any other of his books. Man is admitted into this differentiation, and thus his nature/essence determined.
There is one consequence of the above that I found very interesting and that pops several times in this book; that is the modern tendency to take physics ineligibility to be “ineligibility per se” and to apply it to everything - including man. Way back, Kant transported the understanding of causality from Newtonian physics into the understanding of human freedom as lack of any such causality. During the time Heidegger delivered this course, quantum physics dismissed the notion of causality completely. Heidegger sensed that among physicists, scientists, and philosophers of his time there was an expectation of moving from quantum physics into a quantum biology, and then again further into a quantum history and finally into a quantum metaphysics. Basically, the definition of unpredictability from quantum physics is extended to encompass everything - including human freedom. The reason for this tendency and expectation is quite simple – since quantum physics' predictions were so accurate and fundamental, then they must also be right about everything else. These days there is a lot of talk about quantum computers; and everyone expects, beside and beyond the boost in computing power, some fantastical ontological revelations about nature and in particular about human nature. More generally and for some time now, physics and physicians claim to build a “theory of everything” are taken by almost everyone to really encompass and explain “everything” - including human nature.