Th-debuccalization is a process that occurs in many varieties of Scottish English where /θ/ becomes /h/ word initially and intervocalically.
Th-debuccalization occurs mainly in Glasgow and more generally occurs across the Central Belt. According to Johnston, this feature is becoming more common in these places over time, but is still variable. In word final position, /θ/ is used, as in standard English.
The existence of local /h/ for /θ/ in Glasgow complicated the process of th-fronting there, a process which gives /f/ for historical /θ/. Unlike in the other dialects with th-fronting, where /f/ solely competes with /θ/, in Glasgow, the introduction of th-fronting there creates a three-way variant system of /h/, /f/ and /θ/.
The /θ/ variant is typical of local educated norms (the regional standard), while the use of /h/ and /f/ in place of standard English /θ/ mark the local non-standard norms. /h/ is well-known in Glasgow as a vernacular variant of /θ/ when it occurs word initially and intervocalically, while /f/ has only recently risen above the level of social consciousness.
Given that th-fronting is a relatively recent innovation in Glasgow, hence it was expected that linguists might find evidence for lexical diffusion for /f/ and the results found from Glasgow speakers confirm this. The existing and particular lexical distribution of th-debuccalization imposes special constraints on the progress of th-fronting in Glasgow.
In accents with th-debuccalization, the cluster /θr/ becomes /hr/ giving these dialects a consonant cluster that's doesn't occur in other dialects. The replacement of /θr/ with /hr/ leads to pronunciations like:
See also
three - /hri/
throw - /hro/
through - /hru/
thrash - /hræʃ/
thresh - /hrɛʃ/
threw - /hru/
thrown - /hron/
thread - /hrɛd/
threat - /hrɛt/
throne - /hron/
List of Th-debuccalization homographs