Phoneme hole

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 place of articulation and manner of articulation as possible.

An example of a consonant inventory without holes might be:

p	t	k
b	d	g
f	s	x
v	z	ɣ
m	n	ŋ

while one with several holes might be:

	t	ʈ	k
b		ɖ
f	s	ʂ
m	n	ɳ
ʋ		ɭ	ɣ

Common one-phoneme holes

• Implosives: lack of the velar implosive /ɠ/
• Nasals: lack of the velar nasal /ŋ/
• Stops: lack of the voiced velar stop /g/ (commonly due to lenition)
• Stops: lack of the voiceless bilabial stop /p/ (commonly due to a shift to /ɸ/ → /f/ or /h/)

Impossible phonemes

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