What Brooks and McLuhan found when they met sometime in 1942 or 1943 was a common concern with reality and the conviction that the relation to it implicated more than one human faculty. Cleanth Brooks published ‘History without Footnotes: An Account of Keats’ Urn‘ in the first issue of the Sewanee Review (LII:1) in 1944. Throughout, his concern was with the real and its structure and our apprehension of these.  

the question of real importance [twice repeated on its second page] 90

But is it really a question of truth? 91

the poet provides a sort of realistic basis 94

We are really dealing with an ambiguity here 95

Keats is perfectly aware that the frozen moment of loveliness is
more dynamic than is the fluid world of reality only because it is
frozen. 96

And the poet, by pretending to take the town as real — so real that he can imagine the effect of its silent streets upon the stranger
who chances to come into it — has suggested in the most powerful
way that he can its essential reality for him — and for us. 98

not myth as a pretty but irrelevant make-believe, an idle fancy, but myth as a valid perception into reality. 100

insure our dealing with the problem of truth at the level on which it is really relevant to literature 101