Previous posts have made the case that, for Tolkien, sub-creation at a fundamental level is a kind of “interpretation” of the divine mind and hence being. The question remains, however, as to how this theological perspective might practically inform the sub-creative act. One application, touched on already, is that “humility and an awareness of peril is required”: the function of sub-creation is to explore imaginatively the possible, which is to say, that which is creatable by and therefore imitable of God. As Tolkien implies in his letter to Peter Hastings, a “possible” or “efficacious” world is one that is “possibly acceptable to and by Him!” This means that the act of sub-creation is never a merely theoretical enterprise, a theologically neutral or indifferent speculation into the artistically or aesthetically possible. Rather, every sub-created reality is an implicit statement about who the Creator is and what he is like—a “perilous” venture indeed.
In his essay “On Fairy-Stories” Tolkien develops his criteria for distinguishing good from bad sub-creativity in the realm of Fantasy in more immediately aesthetic or artistic terms, yet the above account enables us to appreciate the theological subtext behind his remarks. As I argued in the series of posts on the role of faith and reason in Tolkien’s fiction, while the reader of a fairy-story must exercise the literary virtue of “secondary belief” when he voluntarily submits himself to the world of the author’s imagining, taking it on its own terms, the author at the same time has the responsibility of imbuing his sub-created, secondary worlds with the kind of “inner consistency of reality” that we find in our own world. The example Tolkien gives is that of a “green sun,” which is relatively easy to imagine but exceedingly difficult to render “credible.” In using the consistency of this world as a measure of any possible sub-created world, Tolkien reflects something of his own Thomistic “actualism,” his conviction, that is, that the world in its actuality is the standard for determining what is possible, and not vice-versa.
On the other hand, Tolkien’s requirement that a sub-created world invite and sustain secondary belief by exhibiting the inner consistency of reality may be further appreciated as a literary application of Aquinas’s three conditions of beauty, namely integrity, harmony, and splendor. This parallel is brought out rather precisely in Rowan William’s summary of these three principles: “integrity, the inner ‘logic’ of a product; then ‘proportion’ or consonance, its harmony and adaptation to the observer’s receptive mind; then splendor or claritas, the active drawing-in of the observing mind.” For Aquinas, any hypothesis that God can do something other than what he in fact does do must of necessity presuppose a context, an alternative potentia ordinata, in terms of which the actualization of that hypothesis might be rendered just or wise. In like manner, we find Tolkien here demanding that the fantastical inventions of a sub-creator be situated within a secondary world in which those inventions might be rendered proportionate. As with God’s own creativity, so with the finite maker’s sub-creativity: the possible is one with the beautiful. Similar to Aquinas, then, who essentially maintains that what God can do or make is the beautiful because only the beautiful has the nature of being and hence of possibility, Tolkien maintains that only an internally consistent and hence beautiful world is to be sub-created because only such a world is creatable by and imitable of the Creator himself. For both Thomas and Tolkien, in summary, every possible world is an ordered world, a world arranged and governed according to a rule or law, and so a world reflecting the justice, wisdom, and goodness of its actual or would-be Maker.
 As Tolkien puts it in his essay, “[c]reative fantasy is founded upon the hard recognition that things are so in the world as it appears under the sun; on a recognition of fact, but not a slavery to it” (TR 74-5).
 Williams, Grace and Necessity, 12.
 Randel Helms represents this fact well in an early study of Tolkien: “My point is that fantasy literature is based on an aesthetic as demanding and uncompromising as any realism. The realistic writer must, to maintain his credibility, make clear (however implicitly) how his events could have happened, for realism stands upon an ontology that grants reality only on a basis of cause-and-effect sequences. Fantasy stands upon a different theory of reality, but one demanding with equal rigor that the fantasist keep always in mind his aesthetic principles: that what happens in his world accord not with his daydreams nor with our own world’s laws of common sense, but with the peculiar laws of the sub-created cosmos.” Helms, Tolkien’s World, 77.