In his Monologion, in which he attempts to demonstrate by reason the things that Christians otherwise hold to be true about God through revelation, Anselm advises his readers that
if I say something along the way that greater authority does not teach, then I wish it to be taken in the following way: it is, indeed, reached as a necessary conclusion from reasoning which seems right to me. Nevertheless, it is not thereby asserted as necessary without qualification. Rather I assert it as possible–for the present at least. (Harrison trans.)
This is curious: Anselm believes that his philosophical, rational, logical arguments for the truth of the Christian doctrine of God possess a certain “necessity,” but he admits that it is a qualified, provisional necessity. What qualifications to his rational theology does Anselm seem to have in mind? I’m not entirely sure, but his phrase “reasoning which seems right to me” may contain at least a partial answer. Although Anselm intends and believes his arguments to be persuasive for an unbeliever, and that they formally do not rely on any revealed premises accessible only by faith, it would be wrong to suppose that Anselm sees himself as operating under the Enlightenment myth of a “pure reason,” i.e., reason without any pre-rational commitments whatsoever. Rather, and as he puts it in his later Proslogion, his philosophical project is a matter of “faith seeking understanding” and an uncovering of the rationes fidei, the “reason” or “rationality” of faith, but which we might with equal justification also identify as the fides rationionis, the “faith of reason” or “reason’s faith.”
More than this, however, because he knows that the rational arguments he is putting forward are not themselves revealed in Scripture, Anselm seems to recognize a sense in which his demonstrations, for all their aspirations to universality and objectivity, are still very much his demonstrations, and should be understood as such, and not just by unbelievers, but especially by his fellow Christians. Anselm hopes and believes his arguments to be rational and true, but this does not absolve his readers of the responsibility of scrutinizing the consistency of his proofs with the authority of revelation (and if and when they should be found to be out of conformity with Scripture, neither should his readers naively criticize Anselm as though he were not acutely aware of that distinct possibility). Thus, while on the one hand excluding any kind of skepticism or relativism in his quest for “necessary” demonstrations, on the other hand Anselm seems to recognize the equally necessary provisionality of reason the moment it ventures (and that by divine permission) from the safe shores of what has been expressly revealed in Scripture.
Another way of characterizing the “possible necessity” of Anselm’s rational theology, I submit, is to see it as an instance of what I have elsewhere referred to as a “sub-creative theology.” In his essay “On Fairy-Stories,” Tolkien argues that human art in general and fairy-stories in particular are “sub-creative” in the sense that, like God in his act of primary creation, they strive to produce “secondary worlds” that nevertheless possess the “inner consistency of reality.” He writes:
What really happens is that the story-maker proves a successful “sub-creator.” He makes a Secondary World which your mind can enter. Inside it, what he relates is “true”: it accords with the laws of that world. You therefore believe it, while you are, as it were, inside.
Similar to Tolkien’s sub-creator, Anselm’s goal in his philosophical theology–whether rationally demonstrating the existence and nature of God in his Monologion and Proslogion, or showing the “necessity” of the Incarnation in his Cur Deus Homo–is to provide an internally consistent and compelling account of Christian truth that at the same time truthfully approximates (if not in fact coincides with) the logic of reality itself as God has made and revealed it. It is in this sense that his theology achieves a “possible necessity”: “necessary” because its own internal, narrative logic leads–with an inexorability that is as much aesthetic as it is “rational”–to the denouement of a Q.E.D.; “possible” because it recognizes reason’s own contingency and fallibility to speak where Scripture itself is silent or at best suggestive.
(It is, incidentally, this recognition of and commitment to a reality that we may asymptotically approach if not exactly capture and reproduce that I suspect differentiates my understanding of “sub-creative theology” from the anti-realist tendencies Francesca Aran Murphy has identified in the 20th and 21st century narrative theologies of “grammatical Thomistis” such as Fergus Kerr and David Burrell and the “story Barthianism” of Robert Jenson and George Lindbeck. See God is Not a Story: Realism Revisited.)