As for the citation from Genealogy of Morals, Nietzsche's genealogical method of historical analysis , which was taken up by Heidegger and Foucault, is not a causal explanation of history. — Joshs

Maybe not. But it is an attempt to use history to claim something beyond fiction. It matters if Nietzsche is correct or not in his reasoning.

Instead, genealogy seeks to illuminate the contingency of what we take for granted, to denaturalise what seems immutable, to destabilise seemingly natural categories as constructs and confines articulated by words and discourse and to open up new possibilities for the future." — Joshs

Yes. That is exactly what Nietzsche said in the portion I quoted, including the part where he says "What can be defined, has no history." That points to a claim about what is the case for us. The critique of metaphysics is put forward to allow for a different kind of explanation. You seem more interested in the critique than the results of his investigation.

When quoting Nietzsche (or anyone), please point to where and what edition you are referring to. Or at least the translator.

"You seem more interested in the critique than the results of his investigation."
Im interested in the method of his investigation, because the results are pre-figured in the method in the sense of how we are supposed to understand the groundedness of those results..
Could you tell me if you are familiar with Karl Popper and the difference between his approach to scientific truth and that of Thomas Kuhn?

Im interested in the method of his investigation, because the results are pre-figured in the method in the sense of how we are supposed to understand the groundedness of those results — Joshs

The properties of ressentiment were "prefigured" by the limits of how ideas could be expressed after Nietzsche critisized Kantian metaphysics?

lets take a break from Nietzsche for a moment. Could you tell me if you are familiar with Karl Popper and the difference between his approach to scientific truth and that of Thomas Kuhn? Or at least, can you tell me what you know of the changes in the way the notion of scientific method has been understood over the past 300 years(deduction, falsificationism, paradigm change, etc)? Do you think there has been no significant change since Newton in how science understands its method? This will help me a lot here.

Sure, we could talk about other things. But what is wrong with what we were talking about before?

We read books and listen to how other people read the same books. Before we can disagree with each other about what is meant, there is this phase where we make sure we are reading the same book. There is very little evidence for me in this thread to suggest we are reading the same book. Or a group of them.

Of course we're not reading the same book. Thats the point. Every word of Nietzsche's you're interpreting according to certain presuppositions and I'm reading him according to an entirely different set of presuppositions. I have an inkling of your presuppositions, but the only way for me to figure out how to translate my terms into yours is by finding out more about your larger presupposotions concerning what science does, what causation means, what objectivity is, etc. I get the sense you think these are obvious and straighforward things, but they are all open to very different interpretations within philosophy of science.

I don't think the ground for science is a straightforward matter. I acknowledge that Nietzsche's critique of objective "facts" would seem to undermine any project he chose to pursue toward the end of establishing some of his own. On the other hand, he does just that. Without apology, qualification, or explanation, he pursues the practice of psychology and places it above others:

All psychology so far has been stuck in moral prejudices and fears: it has not ventured into the depths. To grasp psychology as morphology and the doctrine of the development of the will to power, which is what I have done – nobody has ever come close to this, not even in thought: this, of course, to the extent that we are permitted to regard what has been written so far as a symptom of what has not been said until now. The power of moral prejudice has deeply affected the most spiritual world, which seems like the coldest world, the one most likely to be devoid of any presuppositions – and the effect has been manifestly harmful, hindering, dazzling, and distorting. A genuine physio-psychology has to contend with unconscious resistances in the heart of the researcher, it has “the heart” against it. Even a doctrine of the reciprocal dependence of the “good” and the “bad” drives will (as a refinedimmorality) cause distress and aversion in a strong and sturdy conscience – as will, to an even greater extent, a doctrine of the derivation of all the good drives from the bad. But suppose somebody considers even the affects of hatred, envy, greed, and power-lust as the conditioning affects of life, as elements that fundamentally and essentially need to be present in the total economy of life, and consequently need to be enhanced where life is enhanced, – this person will suffer from such a train of thought as if from sea-sickness. And yet even this hypothesis is far from being the most uncomfortable and unfamiliar in this enormous, practically untouched realm of dangerous knowledge: – and there are hundreds of good reasons for people to keep out of it, if they – can! On the other hand, if you are ever cast loose here with your ship, well now! come on! clench your teeth! open your eyes! and grab hold of the helm! – we are sailing straight over and away from morality; we are crushing and perhaps destroying the remnants of our own morality by daring to travel there – but what do we matter! Never before have intrepid voyagers and adventurers opened up a more profound world of insight: and the psychologist who “makes sacrifices” (they are not the sacrifizio dell’intelletto22 – to the contrary!) can at least demand in return that psychology again be recognized as queen of the sciences,23 and that the rest of the sciences exist to serve and prepare for it. Because, from now on, psychology is again the path to the fundamental problems.
Beyond Good and Evil, 23, Translated by Judith Norman

This juxtaposition of purposes is clearly intended to challenge the reader. He says as much in Ecce Homo where he delights in not helping people fill the gaps. The development of the argument in the On the Genealogy of Morality shows the two un-reconciled elements together where the "objective" arguments reveal some kind of limit to objectivity. The contradiction between the two are placed side by side with each other, as if seating the most contentious members of a family together at Sunday dinner.

I understand that Popper follows up on this topic for the purpose of establishing viable methods in science. He specifically objects to "historicism." Closer than Kuhn to Popper's objection comes from Strauss in his Natural Right and History. They have cogent arguments. I am not sure they would satisfy Nietzsche's criteria of good readers.