If Jewishness is not a metaphysical state, then what is it? Why is a Jew obligated in the commandments while a non-Jew is not? As for conversion, I actually don’t think that’s a problem, because you could say that conversion confers the metaphysical state of Jewishness (like an act of acquisition that confers ownership). By contrast, transmission to descendants used to go through the father and now through the mother, so the question is whether the change in Jewish law is what caused the change in the rules of metaphysics.

The question of why Jewish law obligates specifically Jews really does not require a metaphysical or genetic difference. Just as laws that apply to priests do not require a metaphysical difference between them and us. It is a difference in role, and the Holy One, blessed be He, chose for Himself a people to bear this role, and therefore only we are obligated in this. (Of course, history and that role also shaped us in a certain way, just as every people is shaped by its biography. But that is a result, not a cause.) The question is whether being a chosen people is an innate trait or a mission we received. It seems that Maimonides and the Kuzari disagreed about this. (Aryeh Stern wrote about this in Tzohar, and see there also the responses to his article.)

Beyond that, I have a feeling I still need to work through the idea that saying there is a metaphysical legal effect of acquisition is not the same as saying there is something metaphysically different about a Jew as opposed to a non-Jew.
A first formulation: if you say that the Jew is special because there is a legal status of “Jew” resting on him that obligates him in the commandments, you have not said that he is different in character or superior in some way; you have only defined the metaphysical basis of his obligations, nothing more. When I betroth a woman, I impose on her the legal status of a married woman. That does not change her herself, but only attaches something to her. I am not claiming that I now have before me a different woman in the human sense.

That’s a mistake. Jewish law may have changed (perhaps), but only practically. In terms of the halakhic “truth,” it now becomes clear retroactively that Jewishness was always determined by the mother, and until now we were simply mistaken. (After all, someone who was Jewish because of his father did not remain such after the change in Jewish law.)

D, I really do not agree with that at all.
If at some stage a person was considered Jewish, then he is Jewish forever, even if Jewish law changes. And those who were uprooted from the people were not removed because of their halakhic status, but because in practice they converted and assimilated. (The Sages say that Esau was an apostate Jew.)

See my column 171 about the Ethiopians. In my opinion, a rule somewhat like “a family that has become assimilated remains assimilated” applies here. Someone who was considered Jewish remains Jewish even if the bastards changed the rules (as Nixon said).

Again, you’re talking about practice (“a family that has become assimilated remains assimilated”). What, in your view, is the difference between the Ethiopians whose father is Jewish (let’s say) and an ordinary non-Jew whose father is Jewish? What justifies recognizing them as Jewish and not him?

The justification is very simple: as far as they were concerned, Jewish law (their Jewish law) determined that they were Jewish, and that is indeed how they were supposed to conduct themselves at the time. Therefore we too should recognize that now. What does this have to do with a non-Jew whose father is Jewish? The two cases are not comparable at all.