Phonological change

Under the entry sound law is a rundown of various kinds of sound change, both laws as such and types of change (assimilation, dissimilation, metathesis, etc.) many of which have their own articles.

This article reviews the ways in which phonological systems are affected by sound laws as they act on contrast-points in the system.

In a typological scheme first systematized by Henry Hoenigswald, only four kinds of phonological rearrangement result from sound laws, with a possible fifth (since systematic loss of a sound cannot be accommodated in the scheme present here without awkwardness).

The five phonological rearrangements, then, are:
 * Mere change in pronunciation
 * Primary split
 * Secondary split
 * Merger
 * Loss


 * Note: Primary split would be equally at home categorized as conditioned merger, which is a convenient way of thinking of it (In such a case, "secondary split" would be merely "split").

Mere Change in Pronunciation
Mere change is "mere" in the sense that it involves no reshuffling of the number or distribution of contrasts in a phonological system. For the most part, then, mere changes are examples of allophonic differentiation, i.e., sounds in specific environments acquire new phonetic features or perhaps lose phonetic features they originally had. For example, the devoicing of /i/ and in certain environments in Japanese, the nasalization of vowels before nasal consonants (commonplace, if far from universal), changes in point of articulation of stops and nasals in concert with cavity features of adjacent vowels. "Mereness" inheres in the lack of restructuring, not in the degree of phonetic change: a ramification of original /s/ [s] into would qualify as "mere" as long as all of the phone types remained in complementary distribution.

Many such changes provide the raw ingredients for later, structure-changing innovations. In Proto-Italic, for example, intervocalic *s became *[z]. This was a mere change, a mild and superficial complication in the phonological system only, but when this *[z] merged with *r, the effect on the phonological system was greater (This example will be discussed below under primary split).

Similarly, in the prehistory of Indo-Iranian, the velars *k and *g acquired distinctively palatal articulation before front vowels (*e, *i, *ē *ī). When *e, *o, *a fell together as Proto-Indo-Iranian *a (and likewise *ē *ō *ā as *ā) the result was that the specifically palatal and specifically velar stops now occurred in identical environments: ka and ča, ga and, and so on. This example of secondary split will not be discussed below (Such new contrast points do not remain anchored to their ancestral environments, as a rule; already prehistorically Sanskrit acquired "new" ki, gi sequences via analogy and borrowing, likewise "new" ču,, čm, and similar novelties. And of course the later smoothing of the diphthong *ay to /ē/ had no effect whatever on preceding velar stops).

Most phonological systems are complex affairs with many small adjustments in phonetics depending on phonetic environment, position in the word, and so on, and the great majority of these are the result of mere changes in pronunciation. But not all are. For example, (American) English /r/, and some varieties of British, have a distinctively rounded pronunciation at the onset of stress, particularly at the beginning of a word, regardless of the following vowel (some rounding would be expected before a round vowel): round, rich, reason, rat all begin with (or more accurately ). Indeed, this rounding is salient enough that many small children, and even some adult native speakers, have only a vestigial bunching of the tongue body in such words, or none at all, such that the rounding is all that remains. Put differently, for some such speakers rich and witch are identical, for others there is a phonetic ingredient in rich absent in witch. (This is the "Elmer Fudd" effect: I'll get that wascally wabbit, and so on.) Indeed, in a dialect heard around New York City, becomes, that is, the rounding progresses to a voiced labiodental fricative (but with coarticulated tongue-bunching, such that real and veal remain distinct for such speakers; outsiders might well confuse them).

Now, this rounding feature was not an acquisition via mere change in pronunciation; it's the product of the collapse of the contrast between two earlier phonemes, a rounded r and a plain /r/. This contrast, which from the beginning in Old English was only found in word-initial position, was alive late enough in Middle English to become enshrined in our standard spelling, as wretch vs. retch, wring vs. ring, and all the other words beginning wr- in spelling, faithfully reflecting Old English forms like wrecca "wretch", wringan "to twist", and so on. In the mid-15th century we start finding spelling confusions indicating that the contrast had been lost, but with an unexpected twist: when the contrast between /r/ and collapsed, it was because initial /r/ acquired rounding. That is, what were originally two different phonemes found themselves in complementary (mutually-exclusive) distribution. That is, the features of English r-phonetics are (in part) due to merger, not mere change in pronunciation.

Primary Split
Primary split, or conditioned merger, takes place when some allophones of a phoneme, say A, merge with another phoneme, B. The immediate results are:
 * there are the same number of contrasts as before, but
 * there are fewer instances of A than before, and
 * there are more instances of B than before, and
 * there is at least one environment where A, for the time being, no longer occurs (called a gap)
 * under some circumstances, there will be alternation between A and B, if inflection and derivation result in A sometimes being in the environment in which it merged with B, and sometimes not.

For a simple example, without alternation, early Middle English /dr/ after stressed syllables became /ðr/: módor, fæder (the spelling is deceptive) > mother, father /ðr/, weder "castrated ram" > wether, and so on. Since /ð/ was already a structure-point in the language, this innovation merely resulted in more /ð/ and fewer /d/ and a gap in the distribution of /d/ (albeit not a very conspicuous one).
 * Note 1: thanks to borrowing, from dialects as well as other languages, the original distribution has been disturbed: rudder, adder in Standard English (but obedient forms with /ð/ attested in dialects).
 * Note 2: if you know German, you can figure out which cases of English /ð/ continue original /ð/ and original /d/. Original /d/ corresponds to /t/ in German, original /ð/ corresponds to /d/. Thus wether = German Widder, leather = Leder, brother = Bruder, whether = weder, pointing to original /ð/ in English; weather = German Wetter, father, mother = Vater, Mutter pointing to original /d/.
 * Note 3: alternation between /d/ and /ð/ would have been a theoretical possibility in English, as in sets like hard, harder; ride, rider, but any such details have been effaced by the commonplace diachronic process called leveling.

A trivial example of primary split is the devoicing of voiced stops in German when in word-final position or immediately before a compound boundary:


 * *hand "hand" > /hant/ (cf. plural Hände /hende/
 * Handgelenk "wrist" /hantgeleŋk/
 * *bund "league, association" > /bunt/ (cf. plural Bünde /bünde/)
 * *gold "gold" > /golt/
 * *halb "half" > /halp/ (cf. halben "to halve" /halben/)
 * halbamtlich "semi-official" /halpamtliç/
 * *burg "mountain" /burk/
 * *klug "clever, wise" > /klūk/ (cf. fem. kluge /klūge/)

There were of course also many cases of original voiceless stops in final position: Bett "bed", bunt "colorful", Stock "(walking) stick, cane". Thus, to sum up: there are the same number of structure points as before, /p t k b d g/, but there are more cases of /p t k/ than before and fewer of /b d g/; and there is a gap in the distribution of /b d g/ (which are never found in word-final position or before a combound boundary.


 * Note 1: this split is easily recoverable by internal reconstruction, because it results in alternations whose conditions are transparent. Thus Bund "bunch" (as in, keys) /bunt/ has a plural Bunde /bunde/, in contrast to bunt "colorful" with /t/ in all environments. In a neutralizing environment, such as a voiceless stop in word-final position, one cannot tell which of two possibilities was the original sound. The choice is resolved if the corresponding segment can be found in a non-neutralizing position, as when a suffix follows. Accordingly, a non-inflected form like und "and" is historically opaque (though as the spelling hints, the /t/ was originally *d).


 * Note 2: unlike most phonological changes, this one became a "surface" rule in German, such that loan-words whose source had a voiced stop in the devoicing environment are taken into German with a voiceless one instead: Klub "club" (association) /klup/ from English club. Similarly truncated forms: Bub' (for formal Bube "boy") is /būp/.
 * Note 2a: this surface alternation is what allows modern German orthography to write stops morphophonemically, thus Leib "loaf", Hand "hand", Weg "way", all with voiceless final stops in the simplex form and in compounds, but /b d g/ in inflected forms. Such an orthography is arguably superior to one that writes phonemes as pronounced; in any case, it is a sophistication that came along in the Early Modern period. In Old High and Middle High German voiceless stops were written as pronounced, thus hleip, hant, uuec and so on.


 * Note 3: the exact same distribution holds for /s/ vs /z/, but it arose by a completely different process, namely the voicing of original */s/ between vowels: *mūs "mouse" > Maus /maws/, *mūsīz (for earlier *mūsiz) > Mäuse /moyze/. Original long (now short) ss doesn't voice medially, as in küssen "to kiss" /küsen/, nor does /s/ from Proto-West-Germanic *t, as in Wasser "water" /vaser/, Fässer "kegs" /feser/ plural of Faß /fas/ (= English vat), müßig "idle" /mǖsiç/. German, as in Fisch "fish", reflects original *sk (in native words) and does not become voiced in any environment: Fischer "fisherman" . (German does have , but only in loan-words: Genie "genius", Gage  "salary".)

More typical of the aftermath of a primary split is the famous case of rhotacism in Latin (also seen in some Sabellian language spoken in the same area): Proto-Italic *s > Latin /r/ between vowels: *gesō "I do, act" > Lat. gerō (but perfect gessi < *ges-s- and participle gestus < *ges-to-, etc., with unchanged *s in all other environments, even in the same paradigm). This sound law is quite complete and regular, and in its immediate wake there were no examples of /s/ between vowels except for a few words with a special condition (miser "wretched", caesariēs "bushy hair", diser(c)tus "eloquent": that is, rhotacism didn't take place when an /r/ followed the *s). However, a new crop of /s/ between vowels soon arose from three sources. (1) a shortening of /ss/ after a diphthong or long vowel: causa "lawsuit" < *kawssā, cāsa "house' < *kāssā, fūsus "poured, melted" < *χewssos. (2) univerbation: nisi (nisī) "unless" < the phrase *ne sei, quasi (quasī) "as if" < the phrase *kʷam sei. (3) borrowings, e.g. rosa "rose" /rosa/ from a Sabellian source (the word is clearly somehow from Proto-Italic *ruθ- "red" but equally clearly not native Latin), and many from or through Greek (philosōphia, basis, casia, Mesopotamia, etc., etc.).

A more entertaining example of primary split is the behavior of stops in Latin, voiced and voiceless alike, when immediately followed by a nasal consonant. Such stops became nasals themselves, of the same point of articulation as the original stop, thereby increasing (if only slightly) the inventory of nasals, and creating a gap in the distribution of stops:


 * *sabnyom "Samnium" > Samnium (a region in the southern Apennines)
 * *swepnos "sleep" > somnus (so < *swe is regular)
 * *atnos "year" > annus (cf. Gothic aþna- "year")
 * *supimos "highest" > *supmos > summus

In these cases there is a little reasonably obvious alternation—so Sabīni "Samnites", sopor "(deep) sleep" < *swepor, superior "higher" < *supisyōs, but the history of annus is recoverable only from comparative evidence.

Now, if this pattern holds, we would expect that *gn, *kn would become. What we find are forms like the following:
 * dignus "worthy" < *dek-no-
 * lignum "firewood < *leg-no- (root *leg- "gather"; timber, structural wood, is tignum < *tek-no-, root *tek- "build")
 * agnus "lamb" < *agʷnos or *H₂egʷnos (cf. Greek ámnos "lamb") (In Latin, Proto-Italic labiovelars lose the labial feature adjacent to a consonant, so relictus "left behind" < *likʷ-to- cf. relinquō "leave behind", Greek leipō)

Among the first questions when looking at these forms would be, How would the Romans have spelled if that were the outcome of *kn, *g(ʷ)n? The standard spelling -gn- wouldn't be a particularly obvious choice, which might argue that dorsal stops behave differently from the labials and apicals—the voiceless ones becoming voiced, but no further. However, note that in inscriptions we find highly suggestive non-standard spellings like SINNU = standard signum "sign, insigne", INGNEM = standard ignem accus. sing. "fire". Given this encouraging epigraphic evidence, are there any other reasons for thinking that was in fact the outcome of original dorsal stop plus nasal? There are at least three.


 * 1) The raising of *e to Latin /i/, as seen in these examples, is also seen in cases of *e before certain original, as in tingō "dye, color" < *teng-; quīnque "five" (from *quinque) < *penkʷe; and anyway such a raising is commonplace in diachronic developments (it takes place in Proto-Germanic, as in Old English hring "bracelet, torque", German Ring, < Proto-Germanic *hrengaz revealed by the Finnish borrowing rengas "ring", stem renka-; and in the recent history of English there was another round of such raising, as in ink < Middle English enke, the word English itself.
 * 2) Romance reflexes point to, most clearly Romanian, for example Rom. lemn "wood" < *{{IPA|liŋnu]]. The point is that the regular Romanian reflex of Romance *kt is pt, thus Rom. opt "eight" < *oktu, fapt "deed" < *faktu. That is, dorsal stop plus apical stop becomes labial plus apical, and Rom. mn < Latin gn makes the best sense of the latter stood for . Other Romance languages agree, if less forcefully: in most of them, standard languages and dialects alike, the regular reflex is {{IPA|[ɲ]}}, (palatal nasal). It is not impossible to get from [gn] to {{IPA|[ɲ]}}, of course, but it's a much shorter trip from , which involves nothing more than a mutual assimilation between two points of articulation.
 * 3) The root-forms known from Classical Latin as nō- "know, notice" and nā- "be born" are etymologically gnō- (< *ǵneH₃-) and gnā- (< *ǵenH₁-), as guaranteed by Old Latin forms and copious comparative evidence. In compounds with in- and com-, we find forms like ignōtus "unknown", cognātus "related by birth". The early forms of such compounds would necessarily have been *iŋ-gnō-, *koŋ-gnā-. It is regular for stops to be lost between resonants in Latin, as in ornāre "to adorn" < *ord(i)nāre, pulmentum "food, vittles" < *pelpmentom (and as in these examples, in most such cases the second resonant is a nasal, suggesting intermediate stages like *ornnāre, *pelmmentom.) In any case, the change of *{{IPA|[ŋgn]}} to is in accord with expectations based on other cluster simplifications in Latin.

Note: Roman grammarians, who make some fairly fine observations about Latin phonetics, do not mention g = (their phonetic remarks are always in terms of letters), despite being thoroughly familiar with the idea from Greek orthography, where gamma = {{IPA|[ŋ]}} before /k/ and /g/, as in agkúlos "bent" {{IPA|/aŋkýlos/}}, ággellos "messenger" {{IPA|/áŋgellos/}}. There are several possible explanations for this silence, including mere oversight; but it is entirely possible that much-schoolmastered Standard Latin pronunciation in this regard is an example of a spelling pronunciation that became standard, like the pronunciation of the word figure in American English in place of the original pronunciation rhyming with bigger. The testimony of the Romance reflexes can be taken with greater confidence than the silence of grammarians.

One of the traits of primary split, as outlined above, is that the total number of contrasts remains the same, but it is possible for such splits to reduce the number of contrasts. This happens if all of the primary split products merge with one or another phoneme.

For example, in Latin, the Pre-Latin phoneme *θ (from Proto-Italic *tʰ < PIE *dh) disappears as such by merging with three other sounds: *f (from PIE *bh and *gʷh), *d, and *b:

Initially *θ > f:
 * PItal. *tʰi-n-kʰ- "model, shape" > *θi-n-χ- > Lat. fingō (PIE root *dheyǵh- "smear, work with the hands"; cf. Sanskrit dihanti "they smear", Avestan daēza- "wall" = Greek teîkhos; English dough < OE dág < PIE *dhoyǵh-)
 * PItal. *tʰwor- "door" > *θwor- > Lat. forēs "door" (PIE *dhwor-; like most reflexes plural only; cf Eng. door < *dhur-, Greek thúrā (probably < *dhwor-) usually thúrai pl.)
 * Cf. Latin ferō "carry" < Proto-Italic *pʰer- < PIE *bher-; Latin frāter "brother" < Proto-Italic *pʰrātēr < PIE *bhre-H₂ter-

Medially adjacent to *l, *r, or *u, *θ becomes b:
 * PItal. *wertʰom "word" > *werθom > *werðom (? *werβom) > Lat. verbum (cf. English word < *wurdaⁿ < PIE *wṛdhom, Lithuanian vaṙdas "name")
 * PItal. *rutʰros "red" > *ruθros > *ruðros (? *ruβros) > Latin ruber (via *rubers < *rubrs < *rubros), cf. rubra fem. rubrum neut.
 * PItal. *-tʰlo-/*-tʰlā- "tool suffix" > Latin -bulum, -bula: PIE *peH₂-dhlo- "nourishment" > PItal. *pā-tʰlo- > *pāθlo- > Latin pābulum; PIE *suH-dhleH₂- "sewing implement" > PItal. *sūtʰlā > *sūθlā > Latin sūbula "cobbler's awl"
 * Intervocalic Latin -b- is from PIE *bh, *s, and (rarely and problematically ) *b: Lat. ambō "both" < PIE *ambh- or *H₂embh- (cf. Greek amphi-); Lat. crābrō "hornet" < *ḱṛHs-ron- (cf. Vedic śīrṣn- "hornet"); Lat. cannabis "hemp" (cf. Old English hænep "hemp"). The change of *-sr- to -br- is itself presumably via *-θr- > *-ðr- > *-βr-.

Elsewhere *θ becomes d:
 * PItal. *metʰyo- "middle" > *meθyo- > Pre-Lat. *meðyo- > Lat. medius (three syllables; PIE *medhyo-, cf. Sanskrit madhya-, Greek més(s)os < *meth-yo-)
 * PItal. *pʰeytʰ- > *feyθ- > *feyð- > Lat. fīdus "trusting" (cf. Greek peíthomai "am persuaded", English bid "order, ask")
 * Intervocalic -d- in Latin comes from PIE *d in ped- "foot", sīdere "to sit down", cord- "heart"

There is no alternation to give away the historical story, here, via internal reconstruction; the evidence for these changes is almost entirely comparative reconstruction. But thanks to that reconstruction, we can easily unriddle the story behind the weird forms of the Latin paradigm jubeō "order", jussī perfect, jussus participle; if the root is inherited, it would have to have been PIE *yewdh-.

Secondary Split
In secondary split, a new contrast arises when allophones of a phoneme cease being in complementary distribution and are therefore necessarily independent structure points, i.e. contrastive. This mostly comes about because of some loss of distinctiveness in the environment of one or more allophones of a phoneme. A simple example is the rise of the contrast between nasal and oral vowels in French. A full account of his history is complicated by the subsequent changes in the phonetics of the nasal vowels, but the development can be compendiously illustrated via the present-day French phonemes /a/ and /ã/:
 * Step 1: *a > *ã when a nasal consonant immediately follows: *čantu "song" > (still phonemically );
 * Step 2: at some point in the history of French when speakers consistently stopped making an oral closure with the tongue, we had, that is (if not ) and finally, with the loss of the final stop, modern French  chant "song", distinct from French  chat "cat" solely by the contrast between the nasal and the oral articulation of the vowels, and thus with many other forms in which /a/ and  contrast.


 * Note 1: the nasalization of a vowel before a nasal consonant is found very widely in the world's languages, but is not at all universal. In modern French, for example, vowels before a nasal consonant are oral. That they used to be nasalized, like the vowels before lost nasal consonants, is indicated by certain phonetic changes not always reflected in the orthography: Fr. femme "woman" /fam/ (with the lowering of  (nasalized ) to *ã prior to denasalization.


 * Note 2: unusually for secondary split, the history of the French innovation, even including some changes in vowel cavity features, can be readily inferred by internal reconstruction. This is because the contrastive feature [nasal] in a vowel system usually has a nasal consonant in its history, which makes for straightforward surmises. There are also clear alternations, as "good" (masc.) vs.  (fem.), while such pairs as /fin/ "fine" (fem.) and  (masc.) together with derivatives like rafiné /rafine/ "refined" indicate what happened to nasalized *i.

Secondary split was a major factor in the creation of the contrast between voiced and voiceless fricatives in English. Originally, to oversimplify a bit, Old English fricatives were voiced between voiced sounds and voiceless elsewhere. Thus /f/ was [f] in fisc "fish", fyllen "to fill" [fyllen], hæft "prisoner", ofþyrsted [ofθyrsted] "athirst", líf "life", wulf "wolf". But in say the dative singular of "life", that is lífe, the form was [li:ve] (as in English alive, being an old prespositional phrase on lífe); the plural of wulf, wulfas, was [wulvas], as still seen in wolves. The voiced fricative is typically seen in verbs, too (often with variations in vowel length of diverse sources): gift but give, shelf but shelve. Such alternations are to be seen even in loan words, as proof vs prove (though not as a rule in borrowed plurals, thus proofs, uses, with voiceless fricatives).


 * Note 1: unlike the French example, there is no chance of recovering the historical source of the alternations in English between /s θ f/ and /z ð v/ merely through inspection of the modern forms. The conditioning factor (original location of the voiced alternants between vowels, for example) is quite lost and with little reason to even suspect the original state of affairs; and anyway the original distributions have been much disturbed by analogical leveling. Worthy and (in some dialects) greasy have voiced fricative (next to the voiceless ones in worth and grease) but adjective in -y otherwise do not alternate: bossy, glassy, leafy, earthy, breathy, saucy, etc (cf. glaze, leaves, breathe, and note that even in dialects with /z/ in greasy, the verb to grease always has /s/).


 * Note 2: the phoneme does not alternate with  (and never did). In native words,  is from *sk, and either the change of this sequence to  postdated the rearranging of voicing in pre-Old English fricatives, or else it was phonetically long between vowels, originally, much like the  of present-day Italian (pesce "fish" is phonetically ) and long fricatives, just like sequences of fricatives, were always voiceless in Old English, as in cyssan "to kiss". The Early Modern English development of  < */sj/, as in nation, mission, assure, vastly postdated the period when fricatives became voiced between vowels.


 * Note 3: a common misstatement of cases like OE /f/ > Modern English /f, v/ is that a "new phoneme" has been created. Not so. A new contrast has been created. Both NE /f/ and /v/ are new phonemes, differing in phentic specifications and distribution from OE /f/. Without doubt, one component in this misunderstanding is the orthography. If, instead of speaking of the development of Old English /f/ we said that OE split into /f/ and /v/, there would presumably be less confused talk of "a" new phoneme arising in the process.

It is sometimes claimed that the general account given here, namely that allophones (positional variants) are in effect "stranded" when something changes in the conditioning environment, is incoherent and self-contradictory. The thinking is that if the conditions determining the distribution of a positional variant are lost, the phonetic features of the variant should switch to whatever is called for in the changed environment. That is, when the vowel at the end of OE on lífe "alive" went unpronounced, the [v] allophone of /f/ should have "reverted" in a sense to [f], the form called for in word-final position. This view rests upon a faulty notion of how phonology "works" in the real world of speech acts. A demonstration of this would require elaborate technical discussion; it is perhaps enough to take a look at the example of nasal vowels in French, given above, and ask yourself whether failing to make an oral closure in connection with a phoneme like /m n/, either occasionally or habitually, would really be expected to "cause" the velum to snap shut. For one thing, it hardly could, since it is already open by the time the speaker gets to the point in the speech act where the conditioning factor is (or is not) omitted. And that very fact is instructive for understanding the mechanisms of secondary split.

Merger
Merger, that is, unconditioned (complete) loss of a contrast between two or more phonemes, is not very common. Most mergers are conditioned. That is, if you look closely at most apparent mergers of A and B, you will find an environment or two in which A did something else, like drop or merge with C.

Typical is the merger seen in the Celtic conflation of the PIE plain voiced series of stops with the voiced aspirated series: *bh, *dh, *ǵh, *gh are indistinguishable in Celtic etymology from the reflexes of *b *d *ǵ *g. But the collapse of the contrast cannot be stated in whole-series terms because the labiovelars do not cooperate. PIE *gʷ everywhere falls together with the reflexes of *b and *bh as Proto-Celtic *b, but *gʷh seems to have become PCelt. *gʷ, lining up with PCelt. *kʷ < PIE *kʷ.

Examples of true merger:


 * OE y and ý (short and long high front rounded vowels) fell together with i and í via a simple phonetic unrounding: OE hypp, cynn, cyssan, brycg, fyllan, fýr, mýs, brýd became modern hip, kin, kiss, bridge, fill, fire, mice, bride. There is no way to tell by inspection whether a modern /i ay/ goes back to a rounded or an unrounded vowel. The change is not even reflected in the spelling, since it took place too early to be captured in Middle English Spelling conventions. And of course current spellings like type, thyme, psyche, etc., have nothing to do with OE y = /y/.
 * PIE *l and *r merged totally in Proto-Indo-Iranian, as did PIE *e *o *a into Proto-Indo-Iranian *a. (It might be complained that since the starting points are reconstructed rather than directly observed, these examples aren't cogent. But the reconstructions in question are extremely solid and rest upon evidence which is as massive as it is internally consistent.)
 * The evolution of Romance shows a systematic collection of mergers in connection with the loss of Latin vowel length. Latin had ten vowels, five long and five short (i, ī; e, ē; a, ā; and so on). In the variety of Romance underlying Sardo and some other dialects of the islands, these ten vowels simply fell together pair-wise: in no way are Latin e, ē, say, reflected differently. In Proto-Western-Romance [the ancestor of French, Iberian, Italian north of the Spezia-Rimini line, etc.] however, the story was different. There, Latin /a ā/ fell together totally, as in Sardo, but the other vowels all behaved differently. Upon losing the feature of length, Latin /ī ū/ fell together with nothing. But the short high vowels, front and back, fell together with the long mid vowels: thus Latin /i ē/ are uniformly reflected as PWRom. *ẹ (in the standard Romance notation), likewise /u ō/ become *ọ. PWRom. *ẹ is reflected in French (in open syllables) as /wa/ (spelled oi); voile "sail", foin "hay", doigt "finger", quoi "what", are from Latin vēlum, fēnum, digitus (via *dictu), quid, respectively. There is no way of telling in French which of the two Latin vowels is the source of any given /wa/.

Loss
In Hoenigwald's original scheme, loss—the disappearance of a segment, or even of a whole phoneme—was treated as a form of primary split or merger, depending on whether the loss was conditioned or unconditioned. The "element" that a vanished segment or phoneme merged with was "zero". Now, "zero", a linguistic convention for calling "nothing" a linguistic element, has a certain appeal (albeit an appeal that seems to wax and wane as linguistic theories change). Take the situation where a highly-inflected language has formations without any affix at all: Latin alter "(the) other", for example, is quite endingless, but is specifically nominative singular masculine; cf. altera nom.sg.fem., alterum acc.sg. masc., etc.; it is the only one of the 30 forms that make up the paradigm that is not explicily marked with endings for gender, number, and case. Historically, there is no problem, here. We know that alter is from *alteros (overtly nominative singular and masculine), with the regular loss of the short vowel after *-r- and the truncation of the resulting word-final cluster *-rs. But descriptively it is irksome to say that the "nominative singular masculine" here is signaled by the absence of any affix. More comforting is to view alter as more than what it looks like, viz. /alterØ/, "marked" for case, number, and gender by an affix, just like the other 29 forms in the paradigm. It is merely the case that the "marker" in question is not a phoneme of sequence of phonemes, but the element /Ø/.

So far so good, but one can get into a lot of trouble that way, starting (but from ending) with the philosopical problems inherent in reifying nothing as a kind of "thing" (and a thing with work to do, moreover). Along the way, it is hard to know when to stop positing zeros, and worrisome whether it's rational (or defensible) to regard one zero as different from another: is the zero not-marking can (as in he can) as "3rd person singular" the same zero that not-marks deer as "plural"? Or are both basically a single morphological place-holder of some sort? And once you've decided that there's a zero on the end of deer in three deer, how can you be sure that English adjectives don't agree with the number of the noun they modify, using this same zero affix? (Deictics do, after all: this deer, these deer.) In some theories of syntax it is useful to have an overt marker on a singular noun in a sentence like My head hurts because the syntactic mechanism needs something explicit to generate the singular suffix on the verb; so, are all English singular nouns marked with yet another zero?

It seems preferable to evade all these issues by considering loss as a separate basic category of phonological change, and leave zero out of it.

As stated above, one can regard loss as both a kind of primary spit (when only some expressions of a phoneme are lost) and a disappearance of a whole structure point. The former is much the more common, and is common absolutely.


 * In Latin there are many consonant clusters that lose a member or two: tostus "dired" < *torstos, multrum "milking stool" < *molktrom, scultus "carved" < *scolptos, cēna "dinner" < *kertsnā, lūna "moon" < *louwksnā ("lantern" or the like), and many, many more.


 * Greek lost all stops from the end of a word (so *kʷit "what" > Greek ti, *deḱṃt "ten" > déka, *wanakt "O prince" > ána), but stops generally survive elsewhere. PIE *s drops medially between voiced sounds in Greek, but is preserved in final position and in some consonant clusters.


 * Old English [x] (voiceless dorsal fricative) is everywhere lost as such, but usually leaves something behind. In say furh "furrow", mearh "marrow" it vocalizes. It is gone as such (albeit with varying effects on the preceding vowel, such as lengthening) in night, knight, might, taught, naught, freight, fought, plow (Brit. plough, OE plóh), bought, through, though, slaughter; but /f/ in laugh, trough, tough, enough (and daughter can be found in The Pilgrim's Progress riming with after, indeed the spelling dafter is actually attested)
 * /g k/ are lost in English in word-initial position before /n/: gnaw, gnat, knight, know. /t/ is lost after fricatives before nasals and /l/: soften, often, castle, bristle, chestnut, Christmas, hasten
 * In many words /f/ (that is, Old English [v]) was lost between vowels: auger, hawk, newt < OE nafogar, hafoc, efete ("lizard"), and in some alternative (poetic) forms: e'en "evening", o'er "over", e'er "ever"; Scottish siller "silver", and others.

The ends of words often have sound-laws that apply there only, and many such special developments consist of the loss of a segment. The early history and prehistory of English has seen several waves of loss of elements, vowels and consonants alike, from the ends of words, first in Proto-Germanic, and from there to Proto-West-Germanic, then to Old and Middle and Modern English, shedding bits from the ends of words at every step of the way. There is in Modern English next to nothing left of the elaborate inflectional and derivational apparatus of PIE, indeed of Proto-Germanic, due to the successive ablation of the phonemes making up these suffixes.

Total unconditional loss is, as mentioned, not too common. Latin /h/ appears to have been lost everywhere in all varieties of Proto-Romance. Proto-Indo-European laryngeals survived as consonants only in Anatolian languages, though leaving plenty of traces of their former presence (see Laryngeal theory).