Some people prefer to talk of divine inspiration of Scripture instead of Scriptural inerrance, because they think this way they can avoid affirming inerrance and hence being subject to the apparent counterexamples to inerrance. However, I think the right concept of divine inspiration will make God a full author of the text (so is the human author, of course; I am not here addressing the interaction of the two authorships). Sometimes it happens to an author that the text asserts something that the author did not assert. I doubt this can happen in the case of an omniscient and omnipotent author. If it cannot, then anything that the text asserts is asserted by God. Moreover, it seems central to Christianity and Judaism that God does not lie. Hence, the text only asserts propositions that God believes to be true. But the only propositions that God believes to be true are propositions that in fact are true. Hence, anything the Biblical text asserts is true. If we add some plausible counterfactual robustness to this story (a hard question exactly how to do this—cf. this post), we get inerrance. So inspiration, understood the way I want to understand it, entails inerrance.
I don't mean for the above argument that inspiration entails inerrance (which is basically an expansion of the enthymematic argument for inerrance in Vatican II's Dei Verbum, section 11) to convince those who don't believe inerrance. Rather, I am here interested in a different point. Even if we believe in inerrance, as indeed the Christian Tradition does, nonetheless we have at least two good reasons to focus on inspiration as the basic concept.
First, if we can argue from inspiration to inerrance, but not from inerrance to inspiration, then inspiration is likely to be the more basic concept. If something like the strategy in the first paragraph of this post goes through, we can argue from inspiration to inerrance. But we cannot argue in the opposite direction. Inerrance is a negative doctrine, namely that a text does not contain any false assertions, plus a bit of counterfactual robustness. Such a doctrine could be made true by all kinds of positive realities, of which inspiration is only one. For instance, an uninspired text would be inerrant if, say, God resolves to paralyze the person at the first sign of writing a false. For a more extreme case, God could make a text be inerrant simply by resolving to preventing the human author of the text from setting down any assertions (thus, the text might contain questions, commands, nonsensical rhymes, etc.)
Second, inspiration is a doctrine about all of Scripture. Inerrance is only a doctrine about the truth of assertions in Scripture. An assertion can be true, and intentionally both deeply misleading and spiritually harmful. And there are important portions of Scripture, of varying length, where the main business is is not the making of assertions—but the offering of prayers (especially in the Psalms), the making of commands, the giving of advice ("Go to the ant, O sluggard, and consider her ways, and learn wisdom" is not an assertion), and so on. Inerrance says nothing about those portions. Inspiration does.
Presumably, there is some analogue to inerrance in the case of those portions of Scripture (perhaps, the analogue to inerrance in the giving of proverbial advice is that the advice is helpful when appropriately applied by a phronimos). But these are analogues to inerrance, not inerrance itself, and it is to the doctrine of inspiration that we turn to find out what these analogues would be.
