This post is part of an ongoing series formulating a methodology for tracking and understanding the variety of ways in which early Christians received and utilized Scripture.
The most amorphous and difficult to trace form of thematic correspondence is the thematic echo, where certain words or short phrases used in one text appear in another. These resonances are particularly difficult to place when multiple sources employ the theme or when the text using these echoes employs different themes in close proximity. As an example of multiple possible sources using one theme, consider Romans 10:7, which reads “or ‘Who will descend into the abyss?’” One could argue that here Paul was using Deuteronomy 30:13 (“Who will cross to the other side of the sea for us and get it for us?”), Baruch 3:30 (“Who has gone over the sea, and found her, and will buy her for pure gold?”), or the Wisdom of Ben Sira 24:5 (“Alone I compassed the vault of heaven and traversed the depths of the abyss.”).
While occasionally the surrounding context or verbal dissimilarities with one of the possible sources will delimit these types of citation, often times this is not the case. The prayer in 1 Clement 59-60 provides an example of when a text uses different themes in close proximity to one another. Over the years scholars have argued for references to no fewer than twenty-six different texts in this prayer, although each possible use involves little more than thematic resonance. In such cases, it makes less sense to try and locate a particular source text than it does to simply attribute the reference to thematic similarity. Thematic echoes mark the end of the spectrum of thematic correspondence, where words or ideas are recognizable but contain little more than reminiscence.
 Richard B. Hays, The Conversion of Imagination: Paul as Interpreter of Israel’s Scripture (Grand Rapids: Eerdmans, 2005), 166. Hollander, 89-91.  Hays, Conversion, 164-5. Zahn, “Identifying,” 344. Benjamin D. Sommer, “Exegesis, Allusion, and Intertextuality in the Hebrew Bible: A Response to Lyle Eslinger,” VT 46 (1996): 479-89, esp. 486.  New Revised Standard Version: Harper Collins Study Bible Revised Edition (ed. H.W. Attridge, San Francisco: Harper Collins, 2006). ἤ , Τίς καταβήσεται εἰς τὴν ἄβυσσον; (NA 28).  New English Translation of the Septuagint (ed. B. Wright and A. Pietersma, Oxford: Oxford University Press, 2009). τίς διαπεράσει ἡμῖν εἰς τὸ πέραν τῆς θαλάσσης καὶ λήμψεται ἡμῖν αὐτήν (LXX).  NRSV. τίς διέβη πέραν τῆς θαλάσσης καὶ εὗρεν αὐτὴν καὶ οἴσει αὐτὴν χρυσίου ἐκλεκτοῦ (LXX).  NRSV. γῦρον οὐρανοῦ ἐκύκλωσα μόνη καὶ ἐν βάθει ἀβύσσων περιεπάτησα (LXX).  Gregory and Tuckett’s discussion of thematic echo in the context of determining which Synoptic Gospel stands behind a reference is helpful here, as is their summary of the methodological battle between Edouard Massaux, Helmut Koester, and W.D. Kohler. Gregory and Tuckett, 69-75. See Massaux, Koester, and Kohler.  Prahlow, Appendix A.