Rabbi Professor Michael Broyde has just published an excellent review of Avi Sagi and Zvi Zohar, Transforming Identity: The Ritual Transition from Gentile to Jew—Structure and Meaning. The major argument of the book is that there are two, competitive theories of conversion in rabbinic literature. One requires acceptance of the commandments for conversion, the other does not. [Available here. Hattip: Hirhurim.]
Professor Broyde carefully, respectfully subjects that claim to a critical examination. His findings, based upon razor-sharp reasoning and total control of the full halakhic literature on the subject, arrives at the conclusion that there is absolutely no such tension and that (aside from R. Ben Zion Uziel זצ"ל) there is no precedent for conversion that is totally detatched from a real committment to observance by the convert. (Subsequent observance by the convert, as Rabbi Broyde correctly notes, is a separate issue.)
I admit that I had long been planning to write an article on this subject. However, Rabbi Broyde has 'scooped' me and I am happier for that. Since that is the case, though, I'll add the hiddush that was to serve as the crux of that article.
Much has been made of the fact that there is very little explicit mention in the literature of the requirement that a convert accept the commandments as a sine qua non of conversion. There is far more discussion of the screening process for converts, in terms of their motivation, and of the legal formalities surrounding the act of conversion, itself.
This lacuna is easily explained. It is a given in the History of Law (especially non-constituion-based law), that 'That which goes without saying, usually does,' The tacit assumptions of a legal system, though, are no less binding for their being tacit. Until the Emancipation, being Jewish and observing the commandments were absolutely identical. There was no need to state the obvious. That, indeed, is why references to Qabbalat ha-Mitzvot are all very much en passant. No one EVER questioned its centrality. The operative questions were what (if any) place it had in the actual conversion ceremony (e.g. Bes Din, Tevilla etc.)
What every halakhic authority from Hazal did address was the issue of the motivation of the convert, and the willingness of the convert to acknowledge the full panoply of Jewish observance including, (or more likely, especially) Rabbinic ordinances. It was to that that they need to give their attention. It was only after the Emancipation, when Jewish identity and Jewish observance were no longer, necessarily, identical that the question of conversion and observance arose. Here, in fact there developed an irony. Because the question of observance was an iron-clad, unstated assumption; when it came time to actively inquire whether one needs accept the mitzvot in order to convert, there was no straightforward declaration thereto in the classic sources. This created a situation in which one could begin to argue that less than (or no) such commitment might be feasible (at least, ex post facto). [There are other, agenda driven motives too. These, are addressed by Broyde.] such a position is, however, unfounded and essentially, indefensible from a normative halakhic perspective.