My hermeneutics class has finished reading Grant Osborne's Hermeneutical Spiral and I plan to post my review of it Friday. In the final chapter, we came across Vanhoozer's definition of infallibility and inerrancy, which I thought was very nicely nuanced (and fairly easy to connect to my own understanding). Basically, Vanhoozer would say that the infallibility of the Bible means that God's word invariably accomplishes its purposes. In turn, inerrancy then means that when its purpose is assertion, the proposition of the speech-act is true.
This is very interesting and much more sophisticated than most people who use this language. For example, it recognizes that a good deal of the Bible is not "propositional" in nature. Genesis is a series of narratives, for example. Exodus, Numbers, Joshua through Kings, these are narratives rather than propositions. Sure, one might try to distill them into propositions, but it is a matter for serious debate whether this was their true purpose--at least when we look at the types of propositions that the "propositionalists" want to get from them.
So in what way is Psalm 137 infallible? This is the psalm that ends by applauding anyone who might bash the babies of the Babylonians against a rock. Clearly the purpose of this psalm is not to make propositional assertions. Indeed, this psalm is an expression of great grief. It does not really inform us about God or give us some deep theological truth. To me this psalm tells me that it is okay to cry out to God, okay to vent.
By Vanhoozer's definition, the term infallible applies to Psalm 137, but the term "inerrant" has no meaning because Psalm 137 does not make an assertion.
The word "inerrant" would thus apply only to statements like "God is love" or "If we walk in the light, as He is in the light, we have fellowship with one another..." It would not apply, on the other hand, to "Love your neighbor as yourself," for this is not an assertion but a command. The command is certainly God's command and fully accomplishes God's purposes.