In my latest reading of E.P. Sanders' Jewish Law from Jesus to the Mishnah, Sanders did two things.
1. Sanders
asks a question on page 104: "Did anyone think that halakah was divine
and as binding as the biblical law?" He answers in the negative, and he
focuses on the Mishnah and the Tosefta to argue that the treatment of
the Torah was stricter than the treatment of the halakah and the words
of the scribes. According to Sanders, while it was
believed that some traditions went back to Moses, there did not appear
to be a belief that the entire oral Torah went back to Moses, at least
not from the time of Jesus to the Mishnah. My impression is that such a
notion came later, as even the discussions in academies were eventually considered to have been revealed to Moses on Mount Sinai.
Although
Sanders argues against Jacob Neusner, I think that there are elements
of Neusner's work that overlap with Sanders on this issue. Neusner
argues that there was a time when the authority of the Mishnah was not
self-evident to everyone, and so the Sifra sought to tie the commands
and rulings of the Mishnah to the Torah, which was accepted as
authoritative. But that was one approach, according to Neusner.
Another approach was what is in Avoth: to say that the oral Torah was
revealed on Mount Sinai. (UPDATE: Actually, Avoth just mentions Torah, but many take that to mean the oral Torah. Regarding Neusner's view on Torah in Avoth, I'm writing based on my vague recollection.) Sanders and Neusner appear to
agree that, in the Tannaitic period, it was not always believed that
the halakah was revealed by God to Moses.
(UPDATE: Sanders and Neusner actually disagree on Avoth. Neusner dates it to the mid-third century, whereas Sanders believes that it contains earlier material. Sanders also appears to believe that it's ambiguous in Avoth what the Torah was that was revealed on Sinai and passed down----whether it's legends, teaching in its broad sense, Pharisaic traditions, or Pharisaic interpretations of the written Torah. Sanders does not think that we should conclude from Avoth that the Pharisees put their traditions on par with the written Torah.)
2. Sanders does
not agree with Jacob Neusner that the Pharisees believed that they had
to eat food in a state of ritual purity, necessitating that they wash
their hands before every meal. I talked some about this debate in my post here.
In my latest reading, Sanders focuses on the Pentateuch in addressing
the question of whether ordinary Israelites were required to eat
ordinary food in a state of ritual purity. His conclusion is
that the priests were required to do so, but ordinary Israelites were
not. But Sanders states that, if "wet food...fell on the carcass of a
swarming thing", Israelites could not eat that food (page 148). For
Sanders, that's the only case in the written Torah in which a law of
ritual purity is applied to ordinary, non-consecrated food that was
eaten by ordinary (non-priestly and non-Levitical) Israelites.
Sanders
makes an interesting point on page 148, though. He notes that,
according to Leviticus 17:3-5, Israelites only ate consecrated meat,
since all meat had to be slaughtered at the sanctuary, presented as a
peace offering, and thus "eaten in purity (Lev. 7.19-21)." But
Deuteronomy says the opposite, Sanders states: Because Israel's land was
expanded, Israelites no longer had to have their meat slaughtered at
the sanctuary, and people could slaughter meat in their own locations
and even eat it in a state of ritual impurity. Sanders also
says that, in the first century, Leviticus 17:3-5 was "a dead letter"
and was "dismissed in the Mishnah (Zebahim 14.1-2)."