The standard Orthodox presentation of Written and Oral Torah approximates the following: At Sinai, G-d gave the Jews a section of His wisdom in writing. A different section, for reasons unknown, He whispered into Moshe Rabbeinu’s ears.
There is a subsequent dispute as to the extent of the whispered section, with some describing it as an utterly comprehensive commentary, and others limiting it to the bare minimum principles necessary to develop an authentic Torah commentary, plus some halakhic details, e.g. the blackness of tefillin. All authentic Torah commentary developed later then becomes part of Oral Torah.
All these positions identify the original Oral Torah with a special revelation to Mosheh. Rambam, however, disagreed, and his much more naturalistic position deserves renewed attention in our day.
To understand Rambam’s position, we must begin from the fact that Hashem gave us the Torah in Hebrew. Understanding the Torah therefore requires knowledge of the vocabulary and grammar of Biblical Hebrew. But the Torah does not include a dictionary or a grammar textbook! Rather, G-d gave the Torah to the Jews in Hebrew because they already knew Hebrew.
In other words, the Written Torah is not a self-sufficient document –it is intelligible only on the basis of information that is not in the document itself. We need to learn that information, but the original readers already knew it. So part of the Oral Torah is the linguistic context of the Written Torah as it was known before Sinai by the Jewish people and subsequently passed down to us.
This applies to cultural and historical as well as linguistic knowledge. The Torah was not given to a population with knowledge and awareness of Jewish and general history. The historical and cultural information in Torah is selected from, and given in the context of a much larger set of cultural and historical information, and often can only be fully understood in that context.
Here is one example:
Bamidbar 12:1 informs us that Mosheh had married a Cushite woman. Rashi translates Cushite as beautiful, and offers an array of explanations, including gematria and euphemism, for why Cushit means that here. He accordingly contends that the reference is to Tzipporah, and that Mosheh had only one wife.
Rashbam and Bekhor Shor, however, believe that the reference is to a second wife. They back up their interpretation by citing a historical work (unknown to me) called Divrei haYamim shel Mosheh, in which Mosheh is said to have married an Ethiopian princess, and to have ruled in Ethiopia for forty years.
Rashbam and Bekhor Shor do not cite Josephus (or the Targum attributed to Yonatan ben Uziel), who also brings this story, and Rashi does not cite Targum Onkelos, which translates Cushite as beautiful. But we can be sure that they were choosing among two streams of interpretation with deep Jewish roots.
How do we evaluate these interpretations?
One approach is to see which better helps us resolve other difficulties in the text, such as:
1) What about this relationship disturbed Aharon and Miryam?
2) How is Moshe’s anivut related to this episode?
3) Why does Hashem object to Aharon and Miryam voicing their opinions?
and then decide which interpretation meets them better.
Another approach is to focus on whether it seems more implausible to believe that Cushite means beautiful here, or rather that the Torah mentions a marriage by Mosheh only in passing.
I suggest that both approaches are flawed. The story of Moshe and the Ethopian princess may not derive from the text, either from specific textual phenomena or from the flow of the narrative generally; rather, it may simply have been a biographical fact about Moshe that all original readers knew. It was Oral Torah. It clearly existed in our Masoret even before Churban Bayit Sheni.
Now just as with halakhah, grammar, and lexicography, some parts of the narrative masoret are lost over time. Rashbam and Bekhor Shor, for instance, may not have known a Masoretic source for the story, or even a Jewish source, depending on what their Divrei haYamim shel Mosheh was. I myself first ran across it in a book by the Mormon writer Orson Scott Card.
But while the basic identification of Moshe’s Cushite wife is fundamentally a matter of tradition rather than interpretation, reclaiming Bekhor Shor’s narrative opens up a whole new set of questions. Did Moshe go to Ethiopia as an accepted Egyptian prince, or as part of his escape after killing the Egyptian? Was the marriage a genuine and consummated relationship, or a purely political alliance? These questions can be answered only via creative interpretation, and so the Oral Torah continues to grow.