What Exactly is the Oral Torah?

Does believing that "all Torah is Oral Torah" conflict with the halachic process?

What exactly is the Oral Torah? Over the years I’ve heard people claim it covers everything from Shas and Poskim (the Talmud and codes of halacha) to any derush offered by just about anyone, anywhere. But I haven’t yet come across sources supporting such positions.

There are some obvious problems with the maximalist definitions. Under normal circumstances, for instance, you’re expected to finish your study of the Oral Torah before getting married (Rambam Talmud Torah 1:5). But if all Torah is “Oral Torah”, how can anyone expect to marry within his lifetime?

Another example: a father is responsible for his son’s mastery of both Tanach and Oral Torah. But how much of the Oral Torah? The obligation on the father is absolute (Rambam Talmud Torah 1:1) and whatever curriculum we’re supposed to cover must be complete before the son leaves his father’s sphere of influence - which, from Chazal’s perspective, would probably be the age of 13. But has any father throughout Jewish history ever taught his son “everything” before (or, for that matter, after) bar mitzva?

It’s also useful to recall the way Rambam describes the Torah’s three divisions (“A third Written Torah, a third Oral Torah, and a third…Gemara” - Talmud Torah 1:11) and the way he formulates the Gemara’s instructions for learning Torah (Rambam Talmud Torah 1:12):

Once (a boy) grows in wisdom, he won’t need to learn Tanach or to engage constantly in Oral Torah. (Instead, he should) learn Tanach and Oral Torah (lit. דברי השמועה) from time to time so he doesn’t forget any Torah laws, and devote all his days to Gemara alone…

In fact, based on the Rambam’s own introduction to Mishna Torah, it’s clear that he believed the Oral Torah consisted of nothing more than the complete Mishna and those parts of Talmud Bavli, Talmud Yerushalmi, Sifra, Sifrei, and Tosefta necessary for understanding the Mishna’s halachic conclusions. (This was beautifully explained by R’ Yakov Weinberg in מאורות הרמב”ם - which was written by R’ Weinberg’s students based on his shiurim on the Rambam’s introduction to Mishna Torah.)

Rambam believed that defining and transmitting the Oral Torah is the responsibility of each generation’s bais din hagodol. For the 1,300 years between Moshe at Mt. Sinai and the tannaim Hillel and Shammai, this continued without interruption. But there were no established high courts after Hillel and Shamai. To correct for the risk of chaos, Rabbi Yehuda Hanasi (Rebbi) collected from his contemporaries all the received teachings from the days of Hillel and Shamai and organized them as the Mishna. Because of Rebbi’s status as Av Bais Din, the rulings that make up his Mishna project represent the complete authoritative embodiment of the Oral Torah.

Other Torah works - including Beraissa, Midrash, and parts of the Talmud that aren’t directly clarifying the Mishna - are important, but they’re not part of the Oral
Torah. Instead, most of them would be included in Rambam’s third category: Gemara.

So the Rambam believed that the Oral Torah is a finite and clearly-defined body of work. In fact, the very reason he wrote his Mishna Torah was to provide us with an easily accessible resource for learning the complete Oral Torah curriculum.

Was the Rambam alone in this position? Nope. There’s also the Tur who, in Yore Deah 246, presents a similar approach:

“Torah” refers to the Written Torah - or Tanach. “Mishna” refers to the Oral Torah which includes explanations of the Torah (פירוש התורה). “Talmud” involves understanding and inferring one matter from another…

Now what about the Yerushalmi (Peah 2:4) that suggests Moshe was shown all future Torah thoughts (“אפילו מה שתלמיד ותיק עתיד להורות לפני רבו”)?

There’s no reason to believe that the Yerushalmi is talking about the Oral Torah. I’m sure Moshe knew many things that weren’t even transmitted to his own generation, much less included in the eternal Torah curriculum.