The comparison of parallel versions of a narrative or legal statement in different rabbinic documents may allow us to distinguish between tradition and redaction and to determine the form of a tradition before its inclusion into the broader redactional context. It should be clear, though, that synoptic comparisons of rabbinic texts can never lead to the detection of an “Urtext”, because such an “Urtext” is out of reach, if it ever existed at all. Various versions of a tradition will have circulated at one and the same time, and they will have been constantly changed and adapted to new circumstances. Synoptic comparisons may therefore indicate the main traits of a tradition before its inclusion into the present context, but not the exact words in which it was created or circulated.
Catherine Hezser, “Form-Criticism of Rabbinic Literature”, in The New Testament and Rabbinic Literature, eds. Reimund Bieringer, Florentino García Martinez, Dider Pollefeyt and Peter J. Tomson (Leiden & Boston: Brill, 2010), 104-105.