ConLing - What is vowel harmony?

There come a few times when studying language when you run across something too bizarrely counterintuitive to dream up - to me, vocalic harmony falls squarely in that category. If I didn't know it existed, I'd probably consider it impossible, but there it is, sitting squarely in the middle of Turkish, Igbo, Finnish, and even some dialects of Spanish. But what exactly is it?

Vocalic harmony is when consonant notes are sung simultaneously. jk, that's vocal harmony (wow! vocal, consonant, singing and linguistics get their terminological wires crossed a lot!) This picture was on the Wikipedia page about vocal harmony so, uh... here. It's more entertaining that any of the pictures on the vowel harmony page.

In my post on allophony, I mentioned assimilation, the phenomenon of nearby sounds becoming more alike, usually by sharing an articulatory feature. Assimilation most commonly happens over short distances, typically adjacent segments, but sometimes sounds freak out and decide they have to agree with even far away sounds, extending their assimilatory sensitivites across a whole word - harmony! In languages with harmonic systems, all sounds of a particular type within a given word live in concordant coexistence with one another, usually separating into multiple sets based on a certain feature and only allowing items from one set in each word.

The most common type of harmony happens to vowels, maybe because of the loosey-goosey, spectrum-rather-than-point nature of vowel pronunciation, and essentially any feature of vowel articulation can be subject to harmony (including one that doesn't really exist except to explain harmony - more in a bit). Let me give a few examples.

Everyone's favorite example of vowel harmony is Turkish because it's so neat and easy to understand. Turkish has eight vowels:

If you're not familiar with the "vowel trapezoid," fronter vowels are further to the left and higher vowels are further to the top, with unround vowels written on the left of the dot and round vowels on the right. If you're totally lost here, just know that height, frontness, and rounding are three basic features of all vowels, features on which harmony can seize. Turkish vowels split neatly into pairs based on height, frontness and roundness (the phonemes /y œ ɯ/ are written <ü ö ı>):

Every vowel participates in frontness harmony, with suffixes bending to the frontness of the preceding vowel. For example, the plural suffix -ler/lar can have either an e or an a.

kedi "cat" - kediler "cats" (front)

ayı "bear" - ayılar "bears" (back)

High vowels also participate in rounding harmony, so the ordinal number suffix has four different forms:

iki "two" - ikinci "second" (front unround)

üç "three" - üçüncü "third" (front round)

altı "six" - altıncı "sixth" (back unround)

dokuz "nine" - dokuzuncu "ninth" (back round)

Neat! These examples of Turkish do a pretty good job of illustrating that each item in a harmonic category usually has a counterpart in other harmonic categories, like how a's front counterpart is e here. A common theme of harmonic systems is that affixes will contain a sound underspecified for category, which will appear as the corresponding sound in whatever category the rest of the word follows (like how the plural suffix -l(vowel)r contains a high unround vowel whose harmonic frontness category is determined by earlier vowels).

Frontness and rounding are pretty common subjects for harmony. Another classic example is Finnish, which also has a harmony system based on frontness:

Here, the blue circle is front and the yellow circle is back. Finnish introduces the idea of neutral vowels, shown here in green, which are transparent to harmony - they don't affect the harmonic category of the word, and can exist with both types of vowels. If you're a phonetics buff (or you inspected the Turkish vowels above), you know that e and i are actually front vowels too. For whatever reason, Finnish has decided that even though they are phonetically front, they don't act like it for the sake of harmony. This is not too unusual - harmonic categories don't have to align exactly with phonetic features, and a given language can make its harmony a bit lopsided.

Another very common feature for vowel harmony to work on is "advanced tongue root" (ATR). I'd contend that ATR harmony systems are actually the most common type, but they seem to get less attention because they appear in less familiar languages, and because it's ultimately a harder concept to nail down. This is the one I mentioned that only exists to explain vowel harmony - ATR isn't an absolute feature of a vowel like frontness or rounding, but a spookier one that vowels can only have relative to other vowels. It seems to me like ATR is a combination of frontness, centrality, and height. +ATR vowels are fronter and/or higher and/or less central than their -ATR counterparts.

For instance, here's the vowel system for Igbo:

For the purposes of harmony, /i̙ a u̙ o̙/ are -ATR, contrasting with +ATR /i e u o/.

In terms of morphology, ATR systems work in pretty much the same way as what we've already seen, with affixes aligning with the harmony category of previous vowels. In fact, harmony and affixation seem to go hand-in-hand - languages with more affixing are more likely to exhibit vowel harmony. That makes sense - without affixes, harmony doesn't have anything to operate on. It's also thought that in highly agglutinating languages, where words can get huge, harmony helps to signal word boundaries - if the harmonic category changes, that's a good sign a new word just started.

There are loads of other types of harmony, including some that get consonants involved! Vowels and consonants can both be nasal, giving ample opportunity for harmonization, and it turns out that post-velar consonants get along really well with -ATR vowels, too. For more on that I recommend checking out the Rose and Walker paper.

Doesn't Rose and Walker sound like a hipster restaurant? I think I've got Parker and Otis on the brain.

Further reading:
Wikipedia
Rose and Walker
Metaphony
Umlaut
ATR 
Consonant harmony
Vocal harmony

Languages with vowel harmony:
Turkish 
Finnish 
Igbo 
Mongolian
Warlpiri 
Akan 
Murcian Spanish