What are possible diachronic developments of th sounds?

Of course, I am aware of th-stopping /ð/,/θ/ -> /d/ and of th-fronting/θ/ -> /f/. Are there other developments of ð/ and /θ/ attested in the evolution of natural languages? I am not interested in borrowing and loanword pronunciation, but in internal developments.

3 Answers 3


Proto-Semitic *ϑ becomes /ϑ/ in (classical) Arabic, /t/ in Aramaic and some Arabic dialects, /ʃ/ in Hebrew, /s/ in Amharic, /f/ in some Arabic dialects.

Proto-Semitic *δ becomes /δ/ in (classical) Arabic, /d/ in Aramaic and some Arabic dialects, /z/ in Hebrew, Amharic and Akkadian, etc.

Old Persian /ϑ/ becomes /h/ in Middle and New Persian.

Proto-Iranian *d becomes *δ and then /l/ in Bactrian, Pashto and a few other Eastern Iranian languages.

  • Also, the Hebrew /z/, such as in זה - [ze] - "'this', corresponds to /ð/ in other Semitic languages, which suggests that there might be the shift /ð/>/z/. Aug 11, 2018 at 20:44
  • Didn't I say that?
    – fdb
    Aug 11, 2018 at 20:46

Lateralization to l is also attested in Algonquian and Hawrami Kurdish (questions regarding voicing are not beside the point: in Hawrami the fricative is indeed ð, and in Algonquian it's just the fact that voicing is not contrastive that drives the choice of θ over ð). In North Saami, θ becomes [s] and rumor has it [x], depending on dialect, and this also happened in Spanish. In New Jersey, θ→t̪ which contrasts with t (probably not prestige dialects). Swapping to various fricative places takes place in Athabascan.


Using the searchable version of the Index Diachronica (courtesy of chridd), I found some other possible developments:

  • Proto-Algonquian to Kennebec River Abenaki:
    *θ → n / #_
    *θ → s / _k
    *θ → r

  • Proto-Siouan-Iroquoian to Proto-Siouan:
    *θ → *r

I think it certainly doesn't seem implausible from a theoretical standpoint that an interdental fricative could develop to a rhotic. Unfortunately, both examples of *θ → r in the Index involve reconstructions; I'm not sure if there are any known examples of this sound change being observed more directly.

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