You’ll have heard of the grand old Duke of York. As you know, he had ten thousand men. He marched them up to the top of the hill, and he marched them down again.
It’s thirty-five years since Geoff Pullum wrote an article entitled ‘The Duke of York gambit’, about derivations of the general form A→B→A, that is derivations in which an underlying representation is mapped on to an intermediate form distinct from it, and then on to a surface representation which is identical with the earlier stage. Whether such derivations can be justified synchronically is an issue on which I express no opinion. But there certainly seem to be historical sound changes that proceed in just this way: something changes to something else, then changes back again.
Take popular London English. If Dickens is to be believed, London working-class speakers in the nineteenth century tended to confuse v and w: bevare of vidders! (beware of widows). They certainly don’t now. Historically, w → v → w.
Another well-known, nay stereotypical, Cockney feature is h-dropping. Remarkably, current London yoof — despite the supposed influence of Jamaican English, which shares this feature — generally don’t drop h. So, in the appropriate lexical contexts, h → Ø → h.
Londoners have diphthong shift, no? That is, the PRICE vowel has shifted in popular London speech from aɪ to something in the area of ɑɪ, ɒɪ? And the FACE vowel has gone from eɪ to ʌɪ, æɪ? Not any more. Paul Kerswill, Sue Fox and associates have shown that in inner-London Multicultural London English (blog, 2 July 2010) PRICE has reverted to aɪ and FACE to eɪ (or even eː). So we have aɪ → ɒɪ → aɪ and eɪ → æɪ → eɪ.
If you’ve got the odd twenty minutes to spare, I’d like to recommend this brief talk by Paul Kerswill on just this topic of MLE, given at a TEDxEastEnd event in the wake of the recent rioting.
We like to think of sound changes as typically originating in the working-class speech of big cities, then spreading out socially and geographically. Many of the BrE sound changes of the last 500 years can be explained in this way, with working-class London as the point of departure. But that’s clearly far from the whole story.