Both my younger siblings pronounce "thank" using ð, voicing the "th". I have never heard any other native speaker pronounce it this way. Both my parents, my older sibling, and I all pronounce "thank" using θ, not voicing the "th". I am really wondering where they got this pronunciation form from. From what I have found, the standard pronunciation of "thank" is always with θ.
Has anyone else ever heard "thank" pronounced using ð? Are there any English dialects in which this might be correct?
Essentially the same question was also posted on the linguistics stackexchange, several months after the posting of the present question here on the English stackexchange. As of Jan 14, 2016, here is what we have learned there:
At the present time, there does seem to exist a subgroup of adult native English speakers who pronounce the "th" as voiced. It is not clear if there is any underlying reason for this that would be common to all or even most of them. There do seem to exist some regional tendencies (see 2. below), but it seems there must be some other factors at play as well (see 3. below).
There indeed exists some published research on this: the Survey of English Dialects (Orton et al. 1962-71) recorded "a number of instances of the voicing of all four fricatives in word-initial (Anlaut) position in the South and the South-West Midlands" (Fisiak 1988); see Voitl 1988 (also here). Related research includes that by Martyn Wakelin, esp. Wakelin and Barry (1968) (thanks to Alex B. for all of this).
From the comments by musicallinguist, it seems that sometimes even among siblings raised in the same household (of native English speakers, in an English-speaking country) there can be a difference in the voicing of the initial "th," which then persists into adulthood. References to published research on this aspect would be most welcome.
