Haplololololology

A couple weeks ago, we talked about a process called reduplication, which is when languages double syllables or words to various effect. As with most morphological and phonological processes, there’s a flipside to this coin. (Languages can be a bit like tired, hangry toddlers: indecisive, inconsistent, contrary, and completely beyond being reasoned with.) Sometimes, instead of leaning in to the singsongedness of repeated syllables, languages decide that two syllables are just too similar, and one of them must be eradicated. We call this phenomenon haplology.

I may jest about languages arbitrarily adding or removing syllables, but haplology is actually an elegant remedy for words that may otherwise be cumbersome to pronounce. Consider a few homespun English adverbs: The most common way to form an adverb in English is to add -ly to the end of an adjective. In most cases, this is nothing to bat an eye at. ‘Warm’ becomes ‘warmly’, ‘happy’ becomes ‘happily’, ‘treacherous’ becomes ‘treacherously’. But what about words that already end in [l]? ‘Gentle’ and ‘humble’ become…’gentlely’ and ‘humblely’? Naw. Maybe back in Middle English, but for modern speakers, these adverbs have been streamlined to ‘gently’ and ‘humbly’. They’ve undergone haplology.

There are just some sounds that don’t roll gently off the tongue in quick succession. Another example from English is the pronunciation of ‘February’. Some dialects still carefully pronounce each written sound as in /ˈfɛb.ɹuˌɛɹi/, but that’s a lot of [ɹ]s all piled together. Some dialects have solved the crisis by dissimilation, producing something more akin to /ˈfɛb.juˌɛ(ə)ɹi/. Some UK dialects, though, have solved the problem with haplology instead, resulting in a pronunciation of /ˈfɛb.ɹi/.

A Basque example also shows the elimination of excessive Rs. The word for ‘cider’ comes from ‘sagar’ (apple) + ‘ardo’ (wine). Instead of the compound becoming ‘sagarrardo’, the syllables are simplified, and the result is ‘sagardo’.

Lest you begin to think haplology only happens to liquids like [l] and [ɹ], look at Latin ‘nutrix’ (nurse). It comes from ‘nutrio’ (suckle, predecessor of English ‘nourish’ and ‘nutrition’) + ‘-trix’ (a suffix that formed a female agent noun, like how Amelia Earhart was an aviatrix). The resulting ‘nutritrix’ lost one of its <tri>s—thus, ‘nutrix’.

It has always been a source of great amusement to me (and other linguists—we’re a whimsical lot) that the term ‘haplology’ itself has the potential to undergo haplology, thereby becoming ‘haplogy’. Although this has not actually occurred, haplology is out there, watching over our languages, making some tricky words just a little easier to pronounce.

There be language change afoot–but why?

We’ve written about several big, historic sound changes, like umlaut and Grimm’s Law. But why does pronunciation have to change at all? Why can’t it just stay the same forever? Surely, that would be easier for everyone (especially us historical linguists trying to reconstruct speech from a time before sound recording).

Without diving in too deep today, let’s look at two of the big forces playing tug-o’-war with our phonemes (and the rest of our language): good, old-fashioned laziness and the need to be understood.

I called the first force laziness, but perhaps a kinder appellation would be “conservation of energy.” Unless you live by yourself in a cottage deep in some leafy forest somewhere, you probably regularly do a fair amount of communication (yes, even you introverts). Speech1 is a repetitive motion, and like other repetitive motions (e.g. signing your name), we unconsciously streamline it as it sinks deeper and deeper into our muscle memory. ‘Cannot’ in most instances becomes ‘can’t’; the <tt> in ‘button’ becomes [ʔ] instead of [t].2

This tendency to expend the least amount of effort in language production is called ease of articulation. This is what leads to phenomena like umlaut: it’s easier to pronounce consecutive vowels in the same area of the mouth, so back vowels are pulled forward after front vowels (e.g. Proto-Germanic *mūsiz “mice” becomes OE *mȳs). Similarly, vowels in unstressed syllables tend to relax into schwa. Why enunciate every sound when you don’t really have to? (Except sometimes you do have to.)

Ease of articulation is one thing, but on the other hand, language can’t allow itself to devolve into a mushy, mumbly mess. That would be self-defeating. When your whole purpose in life is to communicate messages, by gum! you’ve got to make sure you can effectively communicate a message. If things become too similar, a language finds ways to self correct, to dissimilate. Dissimilation is a process whereby two linguistic elements that are confusingly alike are pulled back apart to a reasonable, comprehensible distance. Take, for example, the OE pronouns “he” and hēo “she”. Linguists aren’t exactly sure which specific sound change stepped in to shift  hēo to she, but I think we can all agree that it’s easier to tell who’s who with more distinct pronouns. Or in another case, we find the word pilgrim ultimately comes from Latin peregrinus “foreigner, traveler”. In Latin words with far too many /r/s, one of them commonly became an /l/ over time to unmuddy the waters.

Though they seem almost like an uptight, mothering older sister (dissimilation) and her carefree, lackadaisical little brother (ease of articulation), these two processes work in tandem as much as they work against each other. You could almost say they bring balance to the Force. (But you could also say that languages are wild, organic things that refuse to be tied down. It’s not you, it’s them. And as you may have guessed, ease of articulation and dissimilation aren’t the only suspects complicating this situation. We’ll get there.)

Notes

1 It’s something we haven’t brought to the forefront in a while, but I’d like to remind you that when we talk about “speech,” we could just as well be talking about signing. Sign languages function much like spoken languages.
2 Depending on your dialect.

Chaos? Nah, just a vowel shift

Dearest creature in creation,
Study English pronunciation.
I will teach you in my verse
Sounds like corpse, corps, horse, and worse.
I will keep you, Suzy, busy,
Make your head with heat grow dizzy.
Tear in eye, your dress will tear.
So shall I!  Oh hear my prayer.
Pray, console your loving poet,
Make my coat look new, dear, sew it!

 

Just compare heart, beard, and heard,
Dies and diet, lord and word,
Sword and sward, retain and Britain.
(Mind the latter, how it’s written.)
Now I surely will not plague you
With such words as plaque and ague.
But be careful how you speak:
Say break and steak, but bleak and streak;
Cloven, oven, how and low,
Script, receipt, show, poem, and toe.

Finally, which rhymes with enough —
Though, through, plough, or dough, or cough?
Hiccough has the sound of cup.
My advice is to give up!!!

1

Gosh, English pronunciation can be really tricky at times, can’t it? Interested in knowing why?

Well, of course you are! Let’s dive into it together!

As the excerpt above clearly shows, English spelling is often considered a bit ’off’, poorly corresponding to the written word. That’s true, it often doesn’t. But why is that?

Well, while it is not the only reason behind this tricky correspondence between the spoken and written word, today’s topic does explain a lot: the ‘Great’ English Vowel Shift (let’s stick to calling it the GVS from now on) came along and messed things up quite a bit.

Some of you will probably have heard about the GVS before; it was a significant sound change that occurred primarily during the Middle Ages. This sound change affected the long vowels of Middle English, causing them to shift like so:

 

2

Great, so… we done here? You now know everything there is to know about the GVS, right?

Nah, not really.

First, the GVS is actually considered by a lot of linguists to be a process of at least two phases3:

The first phase is considered to have lasted up until approximately the year 1500. During this phase, the long high Middle English vowels /i:/ and /u:/, pronounced similar to the vowels in Modern English meet [mi:t] and lute [lu:t], diphthongised and eventually became the modern English diphthongs /aɪ/ and /aʊ/, the pronunciations you find in mice [maɪs] and mouse [maʊs]. The vowels immediately below them, that is /e:/ and /o:/4, raised one position, falling into the slots previously held by /i:/ and /u:/.

In the second phase, often considered to have been active between the late 16th to mid-17th centuries, the remaining vowels, that is /ᴐ:, a:, ɛ:/, raised one position in height.

What we eventually wind up with is a system of vowels completely changed from its predecessor.

Now, why would that happen?

As with a good number of things in historical linguistics, we don’t exactly know. However, there are two leading hypotheses out there.

The first is the so-called push-chain theory, which was introduced by the great German philologer Karl Luick as early as 1896. Luick argued that the GVS must have been initiated by the movement of the lower vowels /e:/ and /o:/. The two vowels, for some mysterious reason of their own, started to move toward the high vowels /i:/ and /u:/. As they drew nearer, /i:/ and /u:/ started panicking because, it is sometimes argued, they couldn’t raise any higher and remain vowels (instead becoming yucky consonants, bläch).

Well, can’t have that, can we? In pure desperation, /i:/ and /u:/ look for a way out. And they find one—move in (or out, if you will). So, that is precisely what they do, they move in: they become diphthongs, lower and, suddenly, Middle English /i:/ and /u:/ become modern English /əɪ/ and /əʊ/, eventually becoming /aɪ/ and /aʊ/. Tadaa, we have the first steps to a modern English vowel system.

Luick’s hypothesis is actually quite elegant in a way because it successfully explains the lack of diphthongisation of /u:/ in the northern dialects of British English. In these dialects, the vowel /o:/ had previously fronted, becoming /ø:/. The northern dialects therefore didn’t have a vowel /o:/ to push /u:/ out of its place, and the diphthongisation never happened there (pretty neat, huh?).

The second of our hypotheses, the drag-chain theory, was introduced by Otto Jespersen in 1909. Now, Jespersen argued that it was equally likely that the diphthongisation of the high vowels initiated the shift. Basically, Jespersen’s reasoning was like this:

The high vowels, i.e. /i:, u:/, shifted and became diphthongs. That left a ‘gap’ in the vowel system. Horrified, the lower vowels scrambled to move up the ladder to fill the gaps. All of the sudden, Middle English /a:/ became early Modern English /ɛ:/, Middle English /ɛ:/ became early Modern English /e:/ and so on (the back vowels tagged along, too), and so, harmony was restored.

Now, the (to me, at least) flaw of this hypothesis is that it doesn’t account for the non-diphthongisation of northern /u:/, but then again, Luick’s hypothesis claiming that the high vowels couldn’t raise any higher has been noted to be somewhat limited—the high vowels could have done several other things to avoid becoming consonants5. But that’s a different discussion.

Regardless of which of these hypotheses you want to consider more likely, this is the ‘Great’ English Vowel Shift: a huuuuge chain shift that took centuries to complete and affected all long vowels of Middle English. That’s a pretty big deal.

Now, you might be wondering what this has to do with spelling, right? Well, you see, the thing is that English spelling started to become standardized during the ongoing GVS. What this means is that we have a bunch of words where the written form corresponds to a pronunciation that is centuries old. So, basically, meet and meat, both pronounced [mi:t] in British English, are spelled differently because, when those high and mighty people speaking Middle English decided that there was a correct way to spell those words, they did have distinct pronunciations!

So, next time you get annoyed by having to look up how you spell something, just stop and consider that you’re actually spelling the word the way it was pronounced about 600 years ago. Pretty cool, huh?

 

 

 

 

Oh, oh! I almost forgot! Have you been asking yourself why I keep using ‘’ around ‘Great’? No? Well, I’m going to tell you anyway!

The ‘Great’ was introduced by Jespersen and, frankly, while the GVS did indeed have a huge effect on the English language, vowel shifts happen all the time. So, take the ‘Great’ with a pinch of salt and a shot of tequila and we might get on the right track of things.

 

 

 

 

Side notes

1.   There is nothing to say that either of these hypotheses is an accurate description on the initial process of the GVS. Long before I took my first bumbling steps into academia (actually, about a year before I was even born), Donka Minkova and Robert Stockwell noted that it may just be the desire to see a systematic aspect of language and discount its random quirks. So, don’t take it too seriously.

2.     If you’d like to read more about the GVS and other hypotheses, please take a look at Gjertrud Flermoen Stenbrenden’s dissertation work The Chronology and regional spread of long-vowel changes in English from 2010. It’s a really interesting read and introduces a lot more on the subject than I could possibly cover here.

Sources

1 This is an excerpt of the excellent poem The Chaos by Dr. Gerard Nolst Trenité (Netherlands, 1870-1946). Translated by Pete Zakel.

2 This is one of the common ways to depict the GVS, a similar one can be found in most textbooks on the subject. See, for example, Historical Linguistics by Theodora Bynon (1977: 82)

3 See for example The Cambridge History of the English Language (2008) in which Roger Lass writes about this division into two phases. A similar explanation can be found in most textbooks on linguistics that deal, in some way, with historical linguistics (though I really recommend reading Lass’ explanation if you wish to know more about this).

4 Really, I would like to give you examples of these sounds, but I can’t. They’ve basically disappeared from modern English, though they can, most likely, be found in some dialects of English today. Examples can be found of /e:/ in some variants of Scottish English, for example in mate [me:t], but other than that, I can’t seem to find enough examples. If you do find them, though, please let us know! We would love to know more!

5 See, for example the critique by Charles Jones in A History of English Phonology (1989).

Today’s post is brought to you by the letter G

It’s time for the HLC with our very special guest, Proto-Germanic! Yaaay!

Ah, English spelling. That prickly, convoluted briar patch that, like an obscure Lewis Carroll poem, often falls just a little too shy of making sense. Or does it?

It wasn’t always like this. English spelling actually used to be pretty phonetic. People would just write down what they heard or said.1 Then, the printing press was introduced. Books and pamphlets began to be mass produced, literacy levels rose, and spelling began to be standardized. At the same time, English continued to move through some fairly dramatic shifts in pronunciation. The language moved on as the spellings froze.

Throughout the years, people have occasionally called for reforms in English spelling. Like that time in the early 20th century when Andrew Carnegie, Melvil Dewey, Mark Twain, Theodore Roosevelt, et. al. colluded to “improve” some of the more confusing orthographic practices of English. Personally, this linguist is glad such efforts have by and large failed.

Sure, you could look at English spellings and tear at your hair at the monumental insanity of it all. But I like to think of our spellings more as fossils preserving the dinosaur footprints of earlier pronunciations. Granted, sometimes the footprints are from five different species, all overlapping, and there’s, like, a leaf thrown in.

Where are they all going?!

Let’s take, for example, the letter <g>2 and its many possible pronunciations.

First on the menu is the classic [g], a sturdy stop found in words like grow, good gravy, and GIF. This dish originates in the Proto-Germanic (PGmc) voiced velar fricative /ɣ/3. (Refresh your memory on our phonological mumbo-jumbo here.) This velar fricative had a bit of an identity crisis during Old English (OE)4, spurred on by hanging out with sounds all over the mouth.

“But what we found out is that each one of us is a front vowel…and a back vowel…and a palatal approximant…an affricate…and a voiced velar stop…Does that answer your question?”

Around front vowels (such bad influences—triggering umlaut wasn’t enough for them?), it became [j], as in year, from OE ġēar. Between back vowels (the big bullies), it became [w], as in to draw, from OE dragan5. At the end of words, it lost its voicing and became [x] (the sound in loch), as in our own dear Edinburgh (whose pronunciation has since changed again). Ah, but before back vowels, and when backed up by sonorants like [ɹ], it held its ground a little better and became our trusty [g].

As you may have noticed, a lot of the sounds that came from /ɣ/ are no longer spelled with <g>. Alas. We’ll come back to how Edinburgh wound up with an <h> in a minute.

But first, there was another sound that came from PGmc /ɣ/. Old English had something going on called gemination. Sometimes, it would take a consonant and double its pronunciation. Like the <kk> in bookkeeper. Bookkeeper is just fun to say, but these long consonants were actually important back in OE. The wheretos and whyfors of gemination are another story, but just like how /ɣ/ became [j], the geminate /ɣɣ/ was pulled forward and dressed in new clothes as the affricate [d͡ʒ], like in bridge and edge, from OE bryċg and eċg.

Gemination didn’t get around much. It was pretty much restricted to the middle of words. When mushy, unstressed endings began to fall off, the leftovers of gemination found themselves at the end of words, but a little nudge was needed before [d͡ʒ] found its way to the prime word-initial position. Later on in Middle English, the language ran around borrowing far more than a cup of sugar from its neighbor across the Channel. As English stuffed its pockets with French vocabulary, it found a few French sounds slipped down in among the lint. One of those was Old French’s own [d͡ʒ], which on the Continent was simplifying to [ʒ]6 (the <s> sound in measure). This [ʒ] sound didn’t exist in English yet. Our forefathers looked at it, said “nope,” and went on pronouncing it [d͡ʒ]. Thus we get words like juice, paving the way for later words like giraffe and GIF.

This is a GIF. Or is it a GIF? I mock you with my scholarly neutrality.

It was only later, after the end of Middle English, that /ʒ/ was added to the English phoneme inventory, retaining its identity in loanwords like garage and prestige. It’s worth noting, however, that these words also have accepted pronunciations with [d͡ʒ].

Alright, so what about the <gh> in Edinburgh? It turns out there’s another sound responsible for the unpaid overtime of the letter <g>. Meet the sound /h/. In Middle English, Anglo-Norman scribes from France introduced a lot of new spellings, including <gh> for /h/. The <h> part of the <gh> digraph was probably a diacritic meant to indicate a fricative sound. Remember that by this time, the old <g> didn’t really represent a fricative anymore. In words like Edinburgh, the [x] from /ɣ/ had merged with the [x] version of /h/, so it is from /h/ that we get our <gh> spellings. Over time, these [h] and [x] pronunciations weakened and disappeared completely, bequeathing us their spelling to baffle future spelling bee contestants. We have them to thank for bright starry nights, the wind blowing in the high boughs of the trees. But before these sounds went, they left us one last piece to complete our <g> puzzle: after back vowels, sometimes [x] was reanalyzed as [f]. We’ve all been there, right? Your parents say something one way, but you completely mishear them and spend the rest of your life pronouncing it a different way. I mean, did you know the line in the Christmas song is actually colly7 birds, not calling birds? Now imagine that on a language-wide scale. I’m glad for the [f]s. They make laughing more fun, although sometimes convincing your phone not to mis-autocorrect these words can be rough. Had enough? Okay, I’ll stop.

The point of all this isn’t really about the spellings. Just look at all these beautiful sound changes! And this barely scratches the surface. A lot of the big sound changes that warrant fancy names seem to be all about vowels, but as <g> can attest, consonants have fun, too.8 Speaking of big, fancy vowel changes, get your tickets now because next week, Sabina’s going to talk about one of the most famous and most dramatically named: the Great English Vowel Shift.

Notes

1 It wasn’t a perfect system, though. Sometimes, a single scribe would spell the same word several different ways in the same document. Was this reflecting variations in utterances? An inability to decide which letter represented which sound? Transmission errors through copying down someone else’s writing? Who knows.
2 As far as the letter itself goes, the Anglo-Saxons actually used a slightly different symbol known as the insular g. The letter we use today was borrowed from the French during Middle English and is known as the Carolingian g.
3 It’s the voiced version of the sound at the end of Scottish loch. It can be heard today in the Dutch pronunciation of wagon.
4 Refresh yourself on the periods of English here.
5 Actually, draw, drag, and draught/draft are cognates. Knowledge, am I right?
6 This is actually one of my favorite phones. I’m a linguist. I’m allowed to have favorite phones.
7 Because they’re black like coal. And my heart.
8 Admittedly debatable and unnecessarily anthropomorphizing, but we’re already in this thing pretty deep.

Once upon a time…

Once upon a time, there were two brothers who very much enjoyed stories. They travelled their country looking for folk tales, each one darker and grimmer than the last… There was no happily ever after in sight and, though their stories have changed much since, the original tales are still found out there for those brave enough to seek them…

Prepare yourselves, my dears, because this… this is the story of the brothers Grimm.

*

Or not! Actually, it is the story of one of the brothers: Jacob Grimm. And it won’t be grim in the least but full of fun linguistic facts!

Today, we’ll be talking about what is known as the First Germanic Sound Shift, Rask’s Rule or, most commonly, Grimm’s Law.

Riccardo touched upon this topic in last week’s post on the comparative method, a method that was pretty much born with this particular observation. The first to notice the correspondence that would eventually become Grimm’s Law was Friedrich Schlegel, a German philologist, in 1806. Rasmus Rask, a Danish philologist, extended the ‘rule’ to to other PIE languages in 1818 and, eventually, Grimm included German in his book Deutsche Grammatik, published in 1822.

Now, they noticed a regular sound change that affected certain Proto-Indo-European (PIE) consonants. They also noticed that this particular sound change only affected the Germanic languages, e.g. German, Dutch, English, Swedish, etc.

But what is it?

Well, Grimm’s Law describes how certain PIE consonants developed in Proto-Germanic, particularly early Germanic stops and fricatives. Now, you might want to refresh your memory on phonological terminology before continuing, but there can be said to be three parts of the chain shift that is Grimm’s law:

  1. PIE voiceless stops became voiceless fricatives
  2. PIE voiced stops became voiceless stops
  3. PIE voiced aspirated stops became voiced stops or fricatives.

That might be a bit abstract but it basically works like this:

PIE PGmc¹ PIE PGmc PIE PGmc
p > f b > p bh > b
t > θ d > t dh > d
k > x g > k gh > g
> > ghʷ >

 

Consider these words in Latin, English and Swedish and compare them to their PIE root:

 

PIE² Latin English Swedish
*ped- pēs foot fot
*dwo- duo two två
*genu- genū knee³ knä

Now, why would English and Swedish have <f>, <t> and <k> where PIE and Latin have <p>, <d> and <g>?

Well, because English and Swedish, being Germanic languages, underwent Grimm’s Law and thus changed the PIE sound */p/, */d/ and */g/ to /f/, /t/ and /k/ respectively. Latin, on the other hand, is an Italic language and didn’t undergo this change, thus keeping the sounds of PIE (or at least approximately, though exactly how close these sounds are is a bit difficult to say with certainty).  

Why would this happen, you might wonder? What would make one sound shift to become another sound?

Well, we don’t really know exactly how it started or why. It might be what is called a ‘pull chain’, meaning that one sound shifts, leading to a ‘gap’ in the phonological values of the language. As a result, another sound shifts to fill that gap and a third sound shifts to fit the gap of the second one and so on and so forth.

But, it is also possible that it worked the other way around, meaning that one sound started to shift and basically pushed another sound out of its place, thereby leading to a chain shift. This is called a push chain.

But as to how such a chain started? Well, that part is still kind of shrouded in mystery. Perhaps two sounds became too similar to each other and became difficult to distinguish from each other, forcing a shift? We might never know.

What we do know, however, is that Grimm’s Law did affect all Germanic languages, leading to a distinction between that language family and its PIE-derived sisters.

But there are also a good number of exceptions from this rule. For example:

Why does PIE *bʰréh₂tēr (“brother”) become Proto-Germanic *brōþēr but PIE *ph₂tḗr (“father”) became Proto-Germanic *fadēr?

In ‘brother’, the development follows Grimm’s Law, i.e.  t > þ, but in ‘father’ it does not. Instead of the, by Grimm’s law, expected development, i.e. t > þ, the Proto-Germanic word developed t > d. Why is that?

Well, cue Karl Verner; a Danish linguist who in 1875 formulated what is now known as Verner’s Law, an addition, if you will, to Grimm’s Law. Verner’s Law explains such occurrences as ‘father’, showing that voiceless fricatives, e.g. *f, *s, *þ, when immediately following an unstressed syllable in the same word, underwent voicing and becomes fricatives, e.g. *β, *z,*ð

Now, you might be thinking that this is all very interesting but why is it important? ‘cause I can pretty much promise you, that if there is anything the budding historical linguist is aware of, it is Grimm’s Law.

Well, while it is fascinating in its own right, its discovery showed us something much greater than we had ever thought possible before: that sound change is a regular phenomenon, not a random process affecting only some words.

This discovery not only set historical phonology apart as its own field of study but also means that we can predict and understand phonological developments, a discovery that cleared the field for the comparative method.

And without the comparative method, of course, our field of inquiry would be so much poorer as we would largely be unable to properly understand the relationship between languages and the historical developments of those languages.

And wouldn’t we all be a lot poorer for that lack of understanding?

So, next time you watch Cinderella, Little Red Riding Hood or Hansel and Gretel, remember that Jacob Grimm not only provided you with these stories but helped design the most used, and important, method in historical linguistics to this day. Not a bad contribution, right?

Join us next week when our awesome magician Riccardo is back! This time, he’ll be talking about the magic of umlaut and ablaut, so if you’ve ever wondered why it’s ‘mouse’ but ‘mice’ but not ‘house’ and ‘hice’ you definitely don’t want to miss it.

 

Notes and sources

¹ PGmc is a common abbreviation for Proto-Germanic

² All the PIE roots can be found by a simple google search. These are taken from the Online Etymology Dictionary found here: https://www.etymonline.com/. Have fun!

³ Remember now that while the <k> in modern English ‘knee’ is silent today, it was pronounced in earlier stages of English.

*The little pic is from http://tentcampinghq.com/camping-articles/how-to-tell-scary-campfire-stories-2/

**For those who wants to know more about Grimm’s Law, most (if not all) introductory textbooks on linguistics deals with the subject at least a little bit. This particular illustration is from Millward, C.M. A Biography of the English Language.  Ft. Worth: Harcourt, 1996. Pg. 63 but a similar one can be found in pretty much any textbook. Particularly recommended is Lyle Campbell’s Historical Linguistics (3rd ed., 2012) which deals with most things historical linguisticky with great attention to detail and plenty of examples (so it’s recommended generally, not only for this particular sound change).