Farsi does not distinguish between ث (soft 'th' in Arabic, like "think") and ذ (hard 'th' in Arabic, like "that"). A native Farsi speaker pronounces ث like the 's' in "sing" and ذ like the 'z' in "zoo". For example, a Farsi speaker would pronounce Arabic loan words like ثریا and ذوالفقار as as "Soraya" and "Zolfaqar" respectively.

However, I've noticed some Persian words that are written using these consonants--like کیومرث ("Qumars", name) and گذشت ("gozasht", to pass)--but the words are pronounced normally (no 'th' sound).

Why, and what happened? Did Persian (Old, Middle, or New) at some point use 'th' sounds (phonemes?)? That would explain words like "Zarathustra" or "Azar".

Edit: Forgive me if I'm oversimplifying the label "Persian" for the language historically spoken in Iran. I'm an engineer by trade, so I'm not sure when to use Old/Middle/New Persian.

  • 1
    If Old Persian is included in the scope of "Persian" and "ever" then yes. I assume you mean "New Persian", over the past 1200 years.
    – user6726
    Jan 15, 2018 at 5:42
  • Old Persian has "th" sound and classical Persian has "ذ" sound
    – Houman
    Jan 15, 2018 at 10:37

1 Answer 1


There are two different issues here. First: New Persian never had a voiceless /ϑ/, at least not in words of Persian origin (though it is possible that in early Islamic times bi-lingual speakers did pronounce ث correctly as /ϑ/ in Arabic loan words). گيومرث is simply a misspelling of گيومرت which happened to catch on in this proper name. It entered the spoken language from the (wrongly) written form.

Second: Early New Persian did have a voiced /δ/, written ذ, in Arabic loan words, and also in Persian words for etymological post-vocalic /d/. In early manuscripts ذ and د are clearly distinguished. For example in /būδ/ بوذ “he was”. Later (probably in the 12th century) this Persian /δ/ shifted back to /d/ and was written with د. In Arabic words ذ was retained and pronounced /z/. In a small number of genuine Persian words ذ was also retained, and pronounced as /z/. This has a complicated reason, which is discussed here (pp. 94 sqq.):


  • I'm curious why Farsi speakers of English struggle with voiced /δ/ (ie, pronouncing "get the car" as "get de car") if they can pronounce the similar post-vocalic /d (ie, فردا). What about older versions of Persian though? Did Avestan Persian have the soft or hard 'th' sounds?
    – techSultan
    Jan 16, 2018 at 23:20

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