While standard vowel harmony decides which vowels can be roommates based on where they are produced in the mouth (front or back), labial harmony, also known as rounding harmony, organizes them based on whether your lips are rounded or spread. It’s a phonological “rule of attraction” that ensures a word maintains a consistent lip posture from one syllable to the next, creating a distinct, “rounding harmony.”

A Quick Refresher: Palatal (Front/Back) Vowel Harmony

Before we dive into lip rounding, let’s quickly review the more common type of vowel harmony, often called palatal harmony. In Turkish, vowels are divided into two main families:

• Back Vowels: a, ı, o, u (produced towards the back of the mouth)
• Front Vowels: e, i, ö, ü (produced towards the front of the mouth)

The fundamental rule is simple: a word’s vowels must all come from the same family. If the root word contains a back vowel, any suffix added to it must also contain a back vowel. Likewise, front vowels stick with other front vowels. This is why the plural suffix in Turkish has two forms: -lar (with a back vowel) and -ler (with a front vowel).

Consider these examples:

• yol (road) → yollar (roads) – ‘o’ is a back vowel, so the suffix uses the back vowel ‘a’.
• göz (eye) → gözler (eyes) – ‘ö’ is a front vowel, so the suffix uses the front vowel ‘e’.
• kapı (door) → kapılar (doors) – ‘a’ and ‘ı’ are back vowels, so it takes -lar.
• ev (house) → evler (houses) – ‘e’ is a front vowel, so it takes -ler.

This system gives Turkish its melodic, consistent sound. But it’s only half the story.

The Star of the Show: Introducing Labial Harmony

Labial harmony adds a second dimension to this system. It splits the vowels not by their front/back position, but by what your lips are doing when you say them. This gives us two new categories:

• Unrounded Vowels: a, e, ı, i (lips are spread or in a neutral position)
• Rounded Vowels: o, u, ö, ü (lips are pursed into a circle, like for a “w” sound)

The principle of labial harmony states that a rounded vowel in one syllable encourages the vowel in the next syllable to also be rounded. An unrounded vowel, conversely, wants the next vowel to be unrounded. However, the rules in Turkish are more specific and subtle than that. It isn’t a free-for-all; labial harmony primarily influences suffixes that contain high vowels (ı, i, u, ü).

The Rules of the Rounding Game

Think of palatal harmony as the master rule that’s always in effect, and labial harmony as a secondary rule that activates under specific conditions. In Turkish, labial harmony is triggered by a rounded vowel in a root word, but its power is limited.

Rule 1: Low Vowels are Immune

The most important thing to remember is that suffixes containing low vowels (a, e) are completely unaffected by labial harmony. They only obey the front/back rules of palatal harmony.

This is why the plural of yol (road) is yollar, not *yollor*. Even though ‘o’ is rounded, the plural suffix -lar/-ler contains a low vowel (‘a’ or ‘e’) that is immune to rounding. Similarly, the plural of göz (eye) is gözler, not *gözlör*.

Rule 2: High Vowels Must Follow the Leader

Labial harmony comes into play with suffixes that use high vowels. These are suffixes that, depending on the harmony, can appear with one of four vowels: ı, i, u, or ü. The possessive suffixes are a perfect example.

Let’s look at the first-person singular possessive suffix (“my”), which can be -ım, -im, -um, or -üm.

Here’s how the two harmony systems work together to choose the right form:

1. The mouth first asks: “Is the root vowel front or back?” (Palatal Harmony)
2. Then, it asks: “Is the root vowel rounded or unrounded?” (Labial Harmony)

Let’s see it in action:

• Root Word: kız (girl)
  • Vowel is ‘ı’: Back and Unrounded.
  • Resulting suffix: -ım (Back, Unrounded) → kızım (my girl).
• Root Word: dil (tongue)
  • Vowel is ‘i’: Front and Unrounded.
  • Resulting suffix: -im (Front, Unrounded) → dilim (my tongue).
• Root Word: kol (arm)
  • Vowel is ‘o’: Back and Rounded.
  • Resulting suffix: -um (Back, Rounded) → kolum (my arm).
• Root Word: gül (rose)
  • Vowel is ‘ü’: Front and Rounded.
  • Resulting suffix: -üm (Front, Rounded) → gülüm (my rose).

Notice how the rounded vowels in kol and gül “force” the suffix vowel to also become rounded (u/ü). Meanwhile, the unrounded vowels in kız and dil keep the suffix vowel unrounded (ı/i).

Putting It All Together: A Harmony Cheat Sheet

For any 4-way harmony suffix (like the one that produces -lı, -li, -lu, -lü, meaning “with” or “from”), the choice of vowel is determined by the last vowel of the word it attaches to:

• If the last vowel is a or ı (back, unrounded) → The suffix vowel is ı (e.g., tuz → tuzlu, salty; anlam → anlamlı, meaningful).
• If the last vowel is e or i (front, unrounded) → The suffix vowel is i (e.g., şeker → şekerli, with sugar; güç → güçlü, powerful). Wait, ‘ü’ in güç is rounded, yet it takes ‘ü’ -> ‘güçlü’. The rule holds! Let me correct the examples.

Let’s re-do that cheat sheet for clarity:

For a 4-way harmony suffix (like -lı/-li/-lu/-lü):

• If the root vowel is a, ı (Back, Unrounded) → use -lı (e.g., tuz -> tuzlu… no, that’s rounded. akıl -> akıllı, intelligent)
• If the root vowel is e, i (Front, Unrounded) → use -li (e.g., ses -> sesli, loud/with voice)
• If the root vowel is o, u (Back, Rounded) → use -lu (e.g., tuz -> tuzlu, salty)
• If the root vowel is ö, ü (Front, Rounded) → use -lü (e.g., göz -> gözlüklü, with glasses; süt -> sütlü, with milk)

Why Does This Happen? The Linguistics of Laziness

This might seem like a complex set of rules to memorize, but it stems from a very human principle: efficiency. Phoneticians call it coarticulation or, more simply, “articulatory ease.” Our tongues, jaws, and lips are inherently lazy. It’s physically easier to keep the lips in one position (rounded or unrounded) across several syllables than it is to constantly switch back and forth.

When you say the rounded vowel ‘o’ in kol (arm), your lips are already in a rounded position. To pronounce the suffix vowel in kolum (my arm), it’s far easier for your mouth to maintain that rounding and produce a ‘u’ than it would be to unround your lips for an ‘ı’ and then re-round them for the final ‘m’. In essence, your mouth is anticipating the next sound and taking a shortcut.

The Subtle Music of Language

Labial harmony is a perfect example of how languages develop an internal logic that, while seemingly complex, is rooted in the simple mechanics of human speech. It adds a rich, resonant texture to Turkic languages, distinguishing the “ooh” and “ooh” sounds of a word like odunumuz (our firewood) from the flatter “eeh” and “eeh” sounds of evlerimiz (our houses).

So, the next time you hear a Turkish word, listen closely. You’re not just hearing a sequence of sounds; you’re hearing a delicate dance between the front and back of the mouth, and a beautiful rounding harmony conducted by the lips.