The fundamental question of metaphysics.
The question we have identified as first in rank—"Why are there
beings at all instead of nothing?"—is thus the fundamental question
of metaphysics. Metaphysics stands as the name for the center
and core that determines all philosophy.
There Heidegger inserts a note into the lecture's text:
[For this introduction, we have intentionally presented all this
in a cursory and thus basically ambiguous way.
Ending, 2 pages later:
The fundamental question of the lecture course is of a different
kind than the guiding question of metaphysics. Taking Being and
Time as its point of departure, the lecture course asks about the
"disclosedness of Being" (Being and Time, pp. 21 f. and 37 f.). Disclosedness
means: the openedness of what the oblivion of Being
closes off and conceals. Through this questioning, too, light first
falls on the essence of metaphysics, which was also concealed up to
"Introduction to metaphysics" accordingly means: leading into
the asking of the fundamental question.
And MH goes on to lecture about his question, and leaves aside the why, prima causa
, question of metaphysics from Plato to Nietzsche.