Mid central vowel
The mid central vowel (also known as schwa) is a type of vowel sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ə⟩, a rotated lowercase letter e.
While the Handbook of the International Phonetic Association does not define the roundedness of [ə], it is more often unrounded than rounded. The phonetician Jane Setter describes the pronunciation of the unrounded variant as follows: "[ə] is a sound which can be produced by basically relaxing the articulators in the oral cavity and vocalising." To produce the rounded variant, all that needs to be done in addition to that is to round the lips.
Some languages, such as Danish and Luxembourgish, have a mid central vowel that is variably rounded. In some other languages, things are more complicated, as the change in rounding is accompanied with the change in height and/or backness. For instance, in Dutch, the unrounded allophone of /ə/ is mid central unrounded [ə], but its word-final rounded allophone is close-mid front rounded [ø̜], close to the main allophone of /ʏ/.
The symbol ⟨ə⟩ is often used for any unstressed obscure vowel, regardless of its precise quality. For instance, the English vowel transcribed ⟨ə⟩ is a central unrounded vowel that can be close-mid [ɘ], mid [ə] or open-mid [ɜ], depending on the environment.
The mid central unrounded vowel is frequently written with the symbol [ə]. If greater precision is desired, the symbol for the close-mid central unrounded vowel may be used with a lowering diacritic, [ɘ̞]. Another possibility is using the symbol for the open-mid central unrounded vowel with a raising diacritic, [ɜ̝].
Languages may have a mid central rounded vowel (a rounded [ə]), distinct from both the close-mid and open-mid vowels. However, since no language is known to distinguish all three, there is no separate IPA symbol for the mid vowel, and the symbol [ɵ] for the close-mid central rounded vowel is generally used instead. If precision is desired, the lowering diacritic can be used: [ɵ̞]. This vowel can also be represented by adding the more rounded diacritic to the schwa symbol, or by combining the raising diacritic with the open-mid central rounded vowel symbol, although it is rare to use such symbols.