There is a 3 way dispute on Yuma 28b about whether the avos kept all of halakhah, or just those mitzvos already given:

• Rav: The avos kept the entire Torah
• R’ Ashi: … even the rabbinic enactments!
• R Shimi bar Chiya: Avraham only kept the 7 mitzvos benei Noach and beris Milah. (If we’re talking all three avos, presumably the only variation is Yaaqov and his sons keeping gid hanasheh.)

The discussion amongst rishonim is generally found surrounding the verse Bereishis 26:5.

Famously, Rashi holds like Rav Ashi. And this maximalist position has grown to be considered “normative” in many circles. It requires explaining — how did the avos know the Torah’s mitzvos before Sinai and rabbinic rulings and legislation years before the sages who made these decisions did? Did they hold like Rav Moshe Feinstein or Rav SZ Aurbach?  Did they say “morid hatal” in Shemoneh Esrei? (And what does that say, if anything, about the free will of the rabbinate? Or, for that matter, of the notion that both sides of a true halachic dispute are right, each in their own way?)

However, it should be noted that among rishonim, asserting Rav or Rav Ashi’s position as literally true was in the minority. Most rishonim (see discussions on Bereishis 26:5) hold like Rav Shimi bar Chiya. Including: the Rambam (Melachim 9:1), his son R’ Avraham, the Me’iri (intro to Avos), the Ramban, Seforno, Ibn Ezra, Radaq, Chizquni and the Rama (okay, not a rishon). Note the inclusion of the Ramban and Ramba in that list — it’s not just the usual list of names of staunch rationalists rejecting the maximalist position.

A consequence of the rise of the liberal movements is that maximalist hashkafic positions are pushed in some circles so as to avoid their mistake of compromise. Another consequence which feeds this is a focus on studying halakhah to the exclusion of machashevah. (There are other consequences too, but I’ll stick with the relevant ones.) Between these effects, people see Rashi and think that anyone who holds a position embraced by R’ Shimi Bar Chiya, rishonim of both sides of the qabbalah-scholasticism divide, and the Rama is watering down their Torah.

More recently (relatively speaking — going back 110 years or so), a different position emerged — siding like Rav Ashi, but assuming that he didn’t mean that they literally followed every detail.

Rav Chaim Volozhiner writes (Nefesh haChaim 1:21) that the avos were in tune with the needs of their souls, and could see the spiritual impact in all the worlds by their actions, and were thus able to intuit the Torah. And then he concludes that this is why Noach and the avos were not given the Torah. Because, for example, Yaaqov could not marry two sisters nor accomplish the spiritual / metaphysical repairs thereby had the prohibition been commanded already. According to R’ Chaim Volozhiner, “kept the entire Torah” refers to accomplishing the goals of the entire Torah, not that each law of each mitzvah was observed.

R MM Schneerson’s (the 7th Lub Rebbe’s) understanding of R’ Yoseif Yitzchaq Schneerson’s (his father-in-law and predecessor’s) position (Sefer haMaamarim 5697, pg 282, hagah titled “beruchnius velo begashmius“), is similar. That Rav and R’ Ashi aren’t being fully literal and they mean the avos accomplished the spiritual objectives of the mitzvos, and not that for every mitzvah did they physically fulfill it as we would.

Whereas it would seem that most rishonim did understand Rav Ashi literally, whether they personally hold like him or like Rav Shimi bar Chiya. And therefore they bring answers to the question of marrying both Rachel and Leah, and the like. Whether it’s because one of the Noachide mitzvos, which they were obligated in, was thus stronger than the prohibition, or a limitation such as their only following halakhos not yet given when living in Israel.

On the other hand, it is also possible that they took Rav Ashi’s words metaphorically. I posted back in 2009 sources that show that aggadic statements are spoken in metaphor was the norm amongst rishonim and pre-19th century acharonim. (And among later acharonim, I cited R’ Hirsch and R’ Yisrael Salanter.)  There I wrote:

ALL THAT SAID, it seems to be the rules of aggadic stories, even the ones that aren’t historical, that they do not have any of the “good guys” doing something we wouldn’t. And so we still find commentaries trying to justify things on a halachic basis. This shouldn’t be taken to mean they assumed the events actually occurred!

Here too… If Rav Ashi speaks in the metaphor of the avos keeping every last little halakhah, there has to be a way to understand their actions as conforming to that halakhah. If Yaaqov avinu did violate a future Torah law (in our example), then Rav Ashi wouldn’t have made his point using that metaphor.

A consequence of the rise of the liberal movements is that maximalist hashkafic positions are pushed in some circles so as to avoid their mistake of compromise. Another consequence which feeds this is a focus on studying halakhah to the exclusion of machashavah. (There are other consequences too, but I’ll stick with the relevant.) Between these effects, people see Rashi and think that anyone who holds like R’ Shimi Bar Chiya or the Ramban (never mind the staunch rationalists like the Rambam) or who considers Rav and Rav Ashi as speaking metaphorically is watering down their Torah. They both need to keep their Torah maximalist and aren’t investing time studying the other positions.

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1- I like the new (Sep 2012) translation of Nefesh haChaim by R’ Len Moskowitz. (Hebrew in back.) It balances the precision of language really necessary for a philosophical text (even to the extent that yir’ah is consistently rendered “fear/awe”) while still remaining readable. Highly recommended.

2- You’ll notice that most of the links in this post are to pages on he.wikisource.org. I don’t know too many people who use this resource. But is has a complete Chumash with Rashi, Ramban, references to Shas and Rambam and more commentaries, a complete Shas, Rambam, siddurim in various nusachos and even Nefesh haChaim. (Other sefarim are not completed yet. E.g. the edition of Arukh haShulchan is more accurate than any in print, but only for what is filled in so far.)