Perhaps this thread is a little too hung up on the sixpence. The point of the allegory is that the man who has lost a coin is looking for it in completely the wrong place just because that happens to be where the light falls. Modernism casts a light on particular aspects of literary endeavour, and if Shippey's sixpence, be that some sort of artistic truth, a window on the human spirit or other horribly abstract ideal, happens not to be in that place, then Modernism won't find it. Being out in the dark (more likely using the moonlight that Modernism had eclipsed for its followers), Tolkien probably had as much chance of finding sixpence as anybody else. Alternatively he could have found a half-crown, threepence, or an old button, just as could someone using the light. Shippey assumes that critics are looking for something (I seem to recall from his book that it was some sort of literary epiphany) in the wrong place, and that Tolkien, although he may have been equally off target, was at least looking in a different and more logical wrong place.
Humbug, say I. Tolkien was probably not looking for the same coin that an exponent of Modernism might want; in fact he may not have been looking for a coin at all. More likely he wasn't seeking anything in particular, just writing his stories his way, whilst exploring his own philosophy and beliefs through language and legend: it's surprising how few people really think about current critical theory while they write fiction. To adapt one of his own allegories, while others were knocking down the tower to mine for gold, Tolkien was looking for a view of the sea. Neither understood the point of what the other was doing.
As it happens, looking at the present through a filter composed of Christianity and medieval language, myth and literature was nothing particularly new in the 1950s. In fact it was nearly a century out of date: Tolkien's generation was born at the height of the Victorian craze for medievalism, and several of his contemporaries were drawing on the same influences. Clearest to me is Robert Graves, whose poem
Dead Cow Farm draws on the creation legends of
Gylfaginning. T.S. Eliot, who has enjoyed a lot more success than Tolkien in acceptance into high culture, also makes use of medieval literature in
The Waste Land. Perhaps they were looking for the same 'sixpence', but more likely they were looking for cigarette lighters or lost cuff-links.
The upshot of all this is that Shippey's allegory doesn't stand up to intensive examination, but does it really have to? It's clearly intended to demonstrate why twentieth-century (and early twenty-first-century) critical thinking has tended to dismiss his subject, while many often well-educated people, such as Professor Shippey himself, attach to it a greater significance. For me, this sort of argument exemplifies the defiant and provocative tone of this entire book. Its very title invites controversy, and from what I know of the author, he can't have been unaware of that. As for the sixpence, I presume that it's still lying on the pavement undiscovered, presumably next to the solidus that Horace sought.