(Vowel systems)

Here are some phonological universals concerning vowel systems:

Symmetry

• Vowel systems tend to be symmetrical.
• The minimal vowel system includes /i a u/. All known languages are said to have these three vowels, or slight variations of them.

Rounding

• Back vowels tend to be rounded.
• Front vowels tend to be unrounded.

A functional explanation for these vowel universals is that, in its vowel system, a language is likely to use those vowels that are the most perceptually different from one another. This makes it easier for the listener to distinguish between the vowels in the system.

(Consonant systems)

Here are some phonological universals concerning consonant systems:

Symmetry

• Consonant systems tend to be symmetrical.
  • A correlation between point of articulation and voicing of obstruents shows up when there are asymmetries in a consonant inventory.
    • A language is less likely to have voiceless labial obstruents than any other voiceless obstruents.
    • A language is less likely to have voiced velar obstruents than any other voiced obstruents.

• All languages are expected to have at least the following consonant phonemes:
  • Voiceless plosives (stops)
  • Nasals
  • A grooved fricative (for example, /s/)
  • A laryngeal glide (usually /h/)

Voicing

• Most obstruents are voiceless
• Most sonorants are voiced.

(Nasality)

Here are some phonological universals concerning nasality, a process that commonly interacts with both consonants and vowels:

Consonants

• Nearly all languages have nasal consonants.

Vowels

• Nasal vowels are usually the exact counterparts of the oral vowels.
• If a language has fewer nasal vowels than oral, it is usually the mid nasal vowels that are missing.