Jon Rowe has an interesting post at Positive Liberty in which he notes that John Adams once suggested to Thomas Jefferson that the original Decalogue was not Exodus 20:3-17 but instead Exodus 34:14-26 (as a possibility; he explicitly doesn't commit to it). This is actually a view that became fairly common with Wellhausen in his formulation of the documentary hypothesis of the Pentateuch; and Wellhausen himself held that Goethe (from whom Adams derives the suggestion) was a predecessor on this point.* In Goethe the assumption underlying the argument was that the Jewish religion could never have begun with a teaching of such abstract and universal ethics as the Exodus 20 Decalogue; the Jews were a particularistic people, and so their law must have been a particularistic covenant that was only gradually universalized through time. The view is usually seen as also requiring the assumption that Exodus 34:28 refers not to a renewal of the words of Exodus 20 (as seems certainly required by the corresponding account in Deuteronomy), but to the words of Exodus 34 themselves.
There's an article online, by Bernard Levinson, that discusses some of the later history of this proposal of a 'Ritual Decalogue' in higher criticism.
_______
* Goethe's essay on the subject was the Zwo wichtige bisher unerörterte biblische Fragen, which Adams had heard about (but not actually read), and which was published in the collected works. As far as I can tell, the source of Adam's information on the work is unknown. Goethe eventually came to regard his own argument as a rather strange one, resulting more from his reading at the time than from having thoroughly thought the matter out.
