A phoneme hole is a feature of a language's phonology, where an 'expected' phoneme does not occur. What counts as 'expected' is debatable, but at a pinch, a language would be expected to cover as many combinations of its allowed place of articulation and manner of articulation as possible. It should be noted though that most natural languages do have one or more phoneme holes.
An example of a consonant inventory without holes might be:
while one with several holes might be:
The 6 'missing' phonemes would be **/p, d, g, ʂ, ŋ, l/.
Phoneme holes may have at least three basic kinds of history:
- A previous phoneme has changed into another sound, leaving its place vacant.
- In example II, possibly *p → f.
- A phoneme class has arisen in a way that does not allow all possible combinations to arise (perhaps reproducing a hole in another part of the phonology).
- In example II, possibly *ʋ, *ɭ → b, ɖ under certain conditions. Since no alveolar (lateral) approximant **l exists, no **d will exist either.
- In example II, possibly *lt, *ln, *l → ʈ, ɳ, ɭ. If no **ls existed, no **ʂ will arise.
- A hole has persisted as long as a language's history is traceable.
- In example II, possibly no **ŋ ever existed.
A separate phenomenon from phoneme holes is a lack of distinction between certain POA/MOA combinations. A phoneme of this type may be realized intermediate to, or varying between the 'expected' values. In example II, possibly /ɣ/ has an allophone [g] under certain conditions, which would mean that the /g/ slot is not truly vacant.
- The open vowel /a/ is in most languages not subject to the front/back contrast distinguishing /i/ and /u/, or /e/ and /o/. Its realization in any individual language may vary from front [a] to central [ä] to back [ɑ].
- The labial-velar approximant /w/ in most languages contrasts neither with a bilabial approximant nor a velar approximant. In many cases, a more economic analysis than considering it a language's only consonant at the labiovelar place of articulation, is to consider it as simultaneously occypying the labial and the velar POAs.
Common one-phoneme holes
- Implosives: lack of the velar implosive /ɠ/
- Nasals: lack of the velar nasal /ŋ/ or the palatal nasal /ɲ/ (occasionally both)
- Among voiced stops, lack of the backmost member, usually the voiced velar stop /g/ (commonly due to lenition). In languages that have uvular consonants and a voice distinction, the voiced uvular stop /ɢ/ is almost universally replaced by a voiced uvular fricative /ʁ/.
- Among voiceless stops, lack of the voiceless bilabial stop /p/ (commonly due to a shift to /ɸ/ → /f/ or /h/)
Certain POA/MOA combinations are necessarily lacking from human languages due to articulatory constraints. These include, among others:
- Labial laterals
- Glottal nasals
- Voiced glottal stop