Will to Power, Experimental Method

In #36 of Beyond Good and Evil, Nietzsche conducts an "experiment"--the testing of the hypothesis that all causality, volitional, organic, and inorganic, alike, are manifestations of the Will to Power.  In the process, he  implicitly demonstrates that intellectual causality, i. e. inference between propositions, is another such manifestation.  To that extent, the passage covers much of the same ground as does Schopenhauer's exposition of the Principle of Sufficient Reason, i. e. it proposes that the Will to Power suffices as the ground of mechanical, biological, logical, and volitional relations.  However, one process that he cannot validly claim is derived from the Will to Power is the very procedure by which he first establishes that it is a universal ground--the experimental "method".  In other words, by submitting the Will to Power to that method, he presupposes the acceptance of a principle that is independent of it and prior to it, thereby undermining the purported purpose of the passage.