In this part of our little series, we’ll look at some of the sound changes that can affect vowels. Since there tend to be far fewer vowels than consonants in a language’s phonemic inventory, there aren’t as many places for these sound changes to go. For the same reason, however, the vowel system of a language is more prone to change, with new phonemes coming into use and old ones disappearing.
Vowels
Before we begin, think of (or look at) the IPA vowel chart. It’s usually depicted as something like a trapezoid, but it’s just as easy to imagine it as a triangle with vertices at /i/, /a/, and /u/. All the other vowel sounds—/e/, /y/, /ø/, and so on—are along the sides or in the middle. This conception will make a few of the sound changes described below seem more obvious.
Umlaut
The process of umlaut, as found in German, is an example of a larger phenomenon used referred to as fronting. Either term is fine for amateur conlangers, because everyone will know what you mean. Whatever you call it, it’s a change that causes vowels to move towards the front of the mouth.
Most commonly, fronting occurs under the influence of an /i/ sound. (In that, it’s almost like a kind of vowel harmony, or the vowel version of assimilation.) Sometimes, the /i/ later disappears, leaving behind the affected vowel as its only trace.
The Germanic languages embraced fronting to varying degrees, and they’re the best example around. German itself, of course, has the front rounded vowels ü and ö; the diacritic is often called an umlaut for just this reason. Old English, meanwhile, back /ɑ/ was fronted to /æ/. Swedish brought its /uː/ frontward to become /ʉː/. And the list goes on.
Fronting doesn’t always happen, so the back vowels aren’t totally lost. Instead, it can become a way to add in more front vowels; overall, languages tend to have more in the front than the back. Or it can cause mergers, as [y] becomes reinterpreted as /i/. This very thing happened in Greek, for instance.
Raising and lowering
Instead of bringing a vowel to the front, raising brings it up. Usually, this moves a sound one “step” up on the vowel chart: /a/ → /e/ → /i/. Intermediate steps like /ɛ/ can come into play, as well. An example of this process happening right now is in my own dialect of US Southern English, where some vowels are raised before nasal sounds. Thus, “pin” and “pen” sound alike.
The environment usually causes raising, but it’s not any specific sound that triggers it. Nasals can, as they do for me, but raised vowels later in the word can do it, too. So can other consonants. In general, it works out to yet another form of assimilation—vowels will tend to be raised by proximity to other “high” sounds. The reason it works so well for nasals is because they’re the highest in the mouth that you can get: in the nose.
Unlike fronting, raising seems to be more “effective”. But this makes it possible for other sound changes to come into play, sweeping into the vocalic void left behind. If raising gets rid of most instances of /a/, for example, some other sound will likely change to fill that gap.
The opposite of raising, lowering, is one such way of accomplishing this. It’s the same thing as raising, but in reverse: /u/ → /o/ → /a/ is a common trend. Front vowels appear to be harder to lower, likely from the massive influence of /i/, but it’s possible to do, say, /e/ → /ɛ/.
Nasalization
Vowels near nasal sounds might assimilate to them, in a change called nasalization. If the change is thorough enough, it can even result in the loss of the nasal consonant, leaving only a nasal vowel. That was the case in French and Portuguese, both of which have a set of nasalized vowels.
Any of the nasal sounds work for this, from /m/ to /ɴ/, but the “big three” of /n/, /m/, and /ŋ/ are the most common in languages, in that order. They’ll be the likely suspects. If nasalization occurs, then it will probably be on those vowels that precede these sounds; vowels following nasals are less susceptible to the change. Nasals at the end of a word or right before another consonant are the best candidates for the total nasalization that results in their disappearance.
A similar change can occur with /r/-like (rhotic) sounds, but this is much less common. It is a way to get a series of rhotic vowels like those in American English, and it’s conceivable that the difference between “regular” and “rhoticized” could become phonemic.
Lengthening and shortening
Solitary vowel phonemes can, in some cases, become long vowels or diphthongs. On the other hand, it’s easy for those to revert to short vowels. (And those can be shortened further, dropping out altogether, but we’ll get to that in a moment.)
These changes are very connected to the stress pattern of a word. Stressed vowels are more likely to be lengthened or broken into diphthongs. Unstressed vowels, by contrast, get the opposite treatment: reduction and shortening. That’s not the only reason these processes can happen, but it is the primary one.
The total elision of unstressed vowels is also quite possible. This can happen between consonants (syncope), at the beginning of a word (apheresis) or at its end (apocope). All of these are historically attested, both in natural language evolution and in borrowed words. Syncope, for example, occurs in British English pronunciations of words like secretary, while apocope turns American “going” to “goin'”.
Combining and breaking
Two vowels that end up beside each other (probably because of consonant changes) can create an unstable situation. Like the case of consonant clusters, vowel clusters “want” to simplify. They can go about this in a couple of different ways.
The easiest way is for the two to combine into a diphthong or long vowel. Where this isn’t possible, one of the vowels may assimilate to the other, much like consonants. Alternatively, the two might “average out”, fusing into a sort of compromise sound, like /au/ → /o/ (or /oː/, if that’s possible in the language).
Another potential outcome is a separation into two syllables by adding a glide. For example, one form of this diaresis is /ie/ → /i.je/. Once the vowel cluster is broken apart, other sound changes can then alter the new structure, potentially even re-merging the cluster.
Onward
Plenty of other vowel changes exist, but these are the most common and most defining. Next time, we’ll wrap up the series with a look at some of the sound changes that sit outside of the usual consonant/vowel dichotomy, as well as those that can affect a whole word. Also, we’ll conclude with a few rules of thumb to help you get the most out of your conlang’s evolution.