How can geirus (conversion to Judaism) be done without the prospective convert knowing at least the basics of ALL the mitzvos?

Question

When discussing the procedure of conversion to Judaism - Geirus, The Rambam (Hilchos Isurei Biah 14:2) Writes:

וּמוֹדִיעִין אוֹתוֹ עִקְּרֵי הַדָּת שֶׁהוּא יִחוּד הַשֵּׁם וְאִסּוּר עַכּוּ''ם. וּמַאֲרִיכִין בַּדָּבָר הַזֶּה. וּמוֹדִיעִין אוֹתוֹ מִקְצָת מִצְוֹת קַלּוֹת וּמִקְצָת מִצְוֹת חֲמוּרוֹת. וְאֵין מַאֲרִיכִין בְּדָבָר זֶה. וּמוֹדִיעִין אוֹתוֹ עֲוֹן לֶקֶט שִׁכְחָה וּפֵאָה וּמַעֲשֵׂר שֵׁנִי. וּמוֹדִיעִין אוֹתוֹ עונשין שֶׁל מִצְוֹת

And they inform him of the main principles of the religion, which is the unification of God's name, and the prohibition of idol worship, and they dwell at length on this matter. And they inform him of some of the lenient commandments, and some of the stringent commandments. And they do not dwell at length on this. And they let him know the sin of “gatherings” “forgotten sheaves” “corners of the field” and “second tithe.” And they tell him of the punishments for not keeping the commandments.

Since conversion to Judaism is an irreversible undertaking, how can it be done without the prospective convert knowing at least the basics of ALL the mitzvos? We might end up with a situation where a convert was completely misinformed about what accepting Judaism involved, and his conversion would still be valid and irreversible. Why should this be so? What if he says later "It never dawned on me in my wildest dreams that this was included in the practice of Judaism"?

Answer 1

Viewing geirut as spelling out every detail of the b'rit seems impractical. Even many Jews from birth don't know the basics of all the commandments, and while it's reasonable to have a higher bar for those seeking to become obligated, that's an awful lot of learning and testing before the person can enter into the community.

A convert is required to agree to two key principles, kabbalat ol hamitzvot (accepting the yoke of the commandments) and kabbalat ol malchut shamayim (accepting the yoke of heaven). If you truly agree that God is king, that God has given us commandments, and we are obligated to those commandments, then you don't need to know all the details in order to make a decision -- you've already opted in to the system. When you learn that something is forbidden or required you'll follow it, because God commanded it. This is as true for the born Jew who encounters new situations requiring new p'sak as it is for the ger who hasn't learned everything yet or the ba'al teshuva who becomes observant after not being raised that way -- or for all of k'lal yisrael who stood at Sinai and said נעשה ונשמע, we will do and (then) we will understand.

As a practical matter, a rabbi works with a prospective ger for a significant amount of time before the candidate goes before the beit din. During that time the rabbi will probe the candidate in various areas. If he discovers something that might pose a problem, I trust that he would teach those halachot and discuss the matter even if that subject wouldn't otherwise be part of the "curriculum". Nobody involved wants this to end badly, after all.

(No sources, just my own reasoning.)

Answer 2

R. Moshe Feinstein appears to argue that "acceptance of mitzvot" means accepting to be what you think is a proper Jew, even if it does not accord with what in reality is considered a proper Jew, and thus knowledge of specific mitzvot is irrelevant.

Igrot Moshe Y.D. 1:160

ועוד יש מקום לומר טעם גדול דמה שבעלה שנתגיירה בשבילו הוא מחלל שבת ומופקר בכמה איסורין עושה שהיא סבורה שאין חיוב כ"כ לשמור המצות וא"כ הוא כגר שנתגייר בין העכו"ם שמפורש בשבת דף ס"ח שהוי גר אף שעדין עובד ע"ז עיי"ש והטעם משום שקבל עליו להיות ככל היהודים שנחשבה קבלה אף שלא ידע כלום מהמצות דידיעת המצות אינה מעכבת הגרות ורק בידע ולא רצה לקבל הוא עכוב בגרות דהא א"צ ללמד כל התורה כולה קודם שנתגייר דרק מקצת מודיעין

And there is also room to say a great reason, namely, that she converted for the sake of her husband who was a Sabbath-desecrator and free with many prohibitions so she thought that there is not such an obligation to keep the mitzvos. Thus, she is like a convert who converted among the idolaters, about which it is explicit in Shabbat p. 68 that he is a convert even if he still practices idolatry, see there. The reason is that he accepted upon himself to be like all Jews which is considered an acceptance even if he did not know any of the mitzvot, because [lack of] knowledge of the mitzvot does not prevent the conversion. Only by knowing and not wanting to accept is it a prevention of the conversion, because it is not necessary to teach him the whole Torah prior to conversion – we only inform him of some of it. (My translation and emphasis)

Answer 3

The Rambam you cite comes straight from the gemara in Yevamot 47a, which continues

And they do not overwhelm him with threats, and they are not exacting with him about the details of the mitzvot. If he accepts upon himself all of these ramifications, then they circumcise him immediately. [...] When he is healed from the circumcision, they immerse him immediately, and two Torah scholars stand over him at the time of his immersion and inform him of some of the lenient mitzvot and some of the stringent mitzvot. Once he has immersed and emerged, he is like a born Jew in every sense.

So we see that in Talmudic times even the instruction on (some of the!) mitzvot was happening at the end of the conversion process. Remember also how Hillel converted a gentile (Shabbat 31a) before teaching him "That which is hateful to you do not do to another; that is the entire Torah, and the rest is its interpretation. Go study."

The Shulhan Aruch (YD 268:2) builds on the same language and adds "Don't say too much about this [the mitzvot], and don't get too specific either."

The Rambam goes event beyond this and writes (Issurei Biah 13:17) that even if a beit din did not inform a convert of the mitzvot and the punishment for [the failure to observe] the mitzvot and he circumcised himself and immersed in the presence of three ordinary people, he is a (valid) convert. (The SA YD 268:12 disagrees).

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There are at least two ways to explain this

• R Eliezer Melamed here quotes the Schach (268:4) who writes the reason is that even if the convert is sincere, if suddenly confronted with all of the stringencies and fine details, he will recoil and change his mind about converting. Therefore the custom was to convert a candidate after having been taught a few of the minor and major commandments, and after he undertook to keep all the mitzvot. This was the custom in the past, since a convert always joined a religious community. As a result, it was clear that, in principle, he agreed to observe the commandments. Over time he would learn to fulfil them all, even though at the time of conversion he was only aware of part of them.
  
  R Melamed notes that in recent times, as converts don't always join observant communities, they need to spend more time learning the mitzvot so their acceptance is more meaningful.

• R J Simcha Cohen (in How does Jewish law work?, pp. 65ff, online here), brings a number of opinion from R Dovid Hoffman, R Yehiel Yaakov Weinberg (the Sridei Eish) and R Yosef Dov Soloveichik that it is the acceptance of the mitzvot which is critical to legitimize a conversion and a beit din aims to assess if the convert will truly perform the commandments, even if he is - for now - ignorant of law and mitzvot.

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Regarding your last question (what if the convert later says he didn't imagine a certain mitzva could exist?) there is a famous Igrot Moshe (YD 3:108) that if one converts knowing he will be unable to keep one of the mitzvot it is a kosher conversion (cited here).