When he first introduced the term, Sanders did not treat it as a new expression or even as a label:
Within Palestine, ‘normal’ or ‘common’ Judaism was what the priests and the people agreed on. . . . ‘Normal’ Judaism was, to a limited degree, also ‘normative’: it established a standard by which loyalty to Israel and to the God of Israel was measured. . . . Thus whatever we find to have been ‘normal’ was based on internal assent and was ‘normative’ only to the degree that it was backed up by common opinion – which has a good deal of coercive power, but which allows individuals who strongly dissent to break away.” - E.P. Sanders, Judaism: Practice and Belief: 63 BCE - 66 CE (Philadelphia: Trinity Press International, 1992), 47As he acknowledges on the following page, Sanders's definition of common Judaism is indebted to Morton Smith's earlier description of "normative Judaism":
“Down to the fall of the Temple, the normative Judaism of Palestine is that compromise of which the three principal elements are the Pentateuch, the Temple and the ‘amme ha’arez, the ordinary Jews who were not members of any sect.” - Morton Smith, “Dead Sea sect in relation to ancient Judaism,” New Testament Studies 7 (1961): 356.In that article, Smith refers to an earlier essay that he published in 1956, in which he states:
"If there was any such thing, then, as an 'orthodox Judaism,' it must have been that which is now almost unknown to us, the religion of the average 'people of the land.'" - Morton Smith, “Palestinian Judaism in the First Century” in Israel: Its Role in Civilization (Moshe Davis, ed.; New York: Israel Institute of the Jewish Theological Seminary, 1956), 81.
Evidently the question about the core of "normative Judaism" was a live one, because William Farmer, in a book also published in 1956, says something along similar lines, but without the same emphasis on the common people:
“If there were such a thing as ‘normative Judaism’ in the first century A.D., we would have to define it in terms of this national resistance movement, which as we have seen placed so very great importance upon the Land, the Law, and the Temple. Certainly the popular theology of Jesus’ day had its roots in this nationalistic theology which reached back through the Maccabean period into the pre-exilic history of Israel” - W. R. Farmer, Maccabees, Zealots, and Josephus: An Inquiry into Jewish Nationalism in the Greco-Roman Period (Westport, Conn.: Greenwood Press, 1956), 190.
In his 2008 retrospective essay on "common Judaism," Sanders returns to Morton Smith's combination of "the Pentateuch, the Temple, and the ‘amme ha’arez":
"These words seemed totally convincing to me, for the good and simple reason that they corresponded to the evidence. And so I did what I could to reconstruct the Judaism of the common people, paying some attention, of course, to the famous parties but trying to focus on the Petnateuch, the temple, and the ordinary people. I could not use the words 'orthodox' or 'normative,' since both imply control, and I thought that there was relatively little control over what ordinary people did and thought (apart from their activities in the temple). The only term I could think of for Smith's Judaism was 'common Judaism.'" - E.P. Sanders, “Common Judaism Explored” in Common Judaism: Explorations in Second-Temple Judaism (Wayne O. McCready and Adele Reinhartz, eds.; Minneapolis: Fortress, 2008), 17.Sanders was not the first to coin the term, however. If Google serves me right, the first occurrence of the term in an equivalent sense is by the early Jacob Neusner in 1974:
"Before the destruction, there was a common 'Judaism' in the Land of Israel, and it was by no means identical to what we now understand as rabbinic Judaism. The common religion of the country consisted of three main elements, first, the Hebrew Scriptures, second, the Temple, and third, the common and accepted practices of the ordinary folk--their calendar, their mode of living, their everyday practices and rites, based on these first two." - Jacob Neusner, "Introduction" in Understanding Rabbinic Judaism, from Talmudic to Modern Times (Jacob Neusner, ed.; KTAV, 1974), 12.(The statement reappears in essentially the same form in another 1978 essay by Neusner; by 1984 the later Neusner had apparently rejected the idea. The idea of a "common Judaism" is mentioned by Neusner only to be dismissed in 1986.)
- Neusner's formulation of "common Judaism" is clearly a close paraphrase of Morton Smith's 1961 statement about "normative Judaism," but with no acknowledgement anywhere of Smith as the source. (Smith was Neusner's teacher--if I am not mistaken, his Doktorvater.)
- Since Sanders wrote Judaism: Practice and Belief and introduced the concept of "common Judaism" in part to respond to the later Neusner's insistance that we should speak of "Judaisms" in the plural rather than "Judaism" in the singular, it is ironic that the term apparently originated with Neusner himself.