Why does Ramban claim that Rambam does not prohibit the pilegesh for a commoner?

Question

We read in Teshuvot haRashba Meyuchas LehaRamban No. 284:

(….) “And also in regard to the words of the Rambam (Rabbi Moshe ben Maimon), of Blessed Memory, they are not intended to forbid the pilegesh to a commoner and permit it to a king. Rather, this is what he said: “And anyone who has relations with a woman “leshem zenut”, without Kiddushin, is whipped, because he has had sex with a kedesha ; and “leshem zenut” means he contacted and engaged in sex with her and did not render the relationship exclusive to him for the purpose of establishing a pilashut form of relationship, which thus rendered her a kedesha. And Rabbi Moshe of Blessed Memory did not say that anyone who has sex (simply) without Kiddushin is flogged.

And likewise, in his Laws of Kings, when he mentions the issue of pilegesh as it pertains to a king, he does not at all mention that its acceptability applies solely to a king.”

Now, in Laws of Kings 4: 4, Rambam clearly states that pilegesh is forbidden to a commoner: on what grounds then does Ramban say it isn't? I can't understand why. Yaavetz, in his famous response on pilegesh, confines himself to speculating that Ramban was in possession of a different text of the Mishneh Torah, in which the aforementioned prohibition was not there.

Has this topic been investigated by Jewish scholars?

Answer 1

The Ramban, in his letter, directs us to his commentary on Sefer Hammitsvot (footnoted in the edition of this letter in Kitvey Haramban to root 5). However, in his commentary there, he argues against the Rambam and doesn't seem to expand on his understanding of the Rambam's position (in fact, he seems to be oblivious to any possible distinction between a commoner and a king: one of his proofs that a pilegesh is permitted is that King David married some!).

The Kesef Mishne (on Hilchot Ishut 1:4) quotes the Ramban's letter, notes the contradiction, and posits that the Ramban didn't have this line in Hilchot Melachim 4:4 (this is earlier than Ya'avets, to whom you attribute the same idea).

The Lev Sameach (on Sefer Hammitsvot, root 5, ד"ה אבל הרמב"ן ז"ל and following paragraphs) thinks that the Ramban just misunderstood the Rambam.