The process in which one sound becomes more like a nearby sound is called assimilation. In assimilation mostly one sound changes but what is the process in which two sounds are changed? Consider the following example from Persian:

masjed- مسجد changes to masĉed and then changes to maĉĉed - مچد

meaning: Mosque

This process, I presume, is called همگونی دوسویه which loosely translates into bidirectional assimilation. In general when does it happen? And how should we detect them?

  • Could you clarify what you think how the two sounds are changing? From how you've presented it, it looks like /s/ changes to [tʃ] before another /tʃ/, which just looks like a simple case of one assimilation. This is touched on by user6726 below, but I think you should edit to clarify your question. Mar 9, 2016 at 16:54
  • There are two processes you see the word is (as it is written) /masjed/ in the first step it is changed into /masĉed/ and in the second /maĉĉed/. I have some references which states that it is mutual/reciprocal assimilation but the definition of reciprocal assimilation, as user6726 states, is different. Mar 10, 2016 at 6:50
  • I have revised my question Mar 10, 2016 at 10:26
  • I've taken your factual claim at face value, but now that your question has changed, it would be appropriate to explain your evidence, especially the chronological sequencing. We can take it for granted that the historical input is Arabic masjid. The Forvo token has the original consonants. So what do you mean / what is your evidence, when you say it changes to masčed, and 'then' changes to maččed. What kind of changes are you talking about?
    – user6726
    Mar 10, 2016 at 16:41
  • @user6726 exactly the original word is /masjed/. The change it what we hear in today's Persian. I read it in a book that this case is mutual assimilation. but I wondered if this word fall into the same category. Mar 10, 2016 at 18:03

2 Answers 2


I don't know of a standard term. I'd refer to it as mutual assimilation. The change in Sanskrit of ai to ee = e: is an example. So far as I know, there's nothing special about it, as compared with other assimilations, except that it's, well, mutual.


"Bidirectional assimilation" is an unlikely name for that kind of case, which constitutes "gemination" or "geminate formation". "Bidirectional assimilation" is generally used for the assimilation of a property which both affects a segment on the left and a segment on the right. ATR and nasal harmonies are the canonical examples, where e.g. /wemao/ → [w̃ẽmãõ].

When the result of combining two distinct adjacent segments is a single long segment, we usually refer to the process as merger or fusion, possibly adding a form of the word "geminate" to indicate that the result is a geminate consonant (for instance, /hy/ → [ʃʃ]). In the specific example you give, no feature is contributed by /s/, and /tʃ/ doesn't become in any way "more like" the deleted /s/. You might encounter a case that could be called reciprocal assimilation, where in a sequence of segments /AB/, A takes some property from B and B takes some property from A, and the result is surface DE (not a geminate). The most common case of that kind involves progressive post-nasal voicing, and regressive place assimilation, whereby /mk/ → [ŋg]. However, this is not "a bidirectional assimilation", it is two assimilations, one regressive and the other progressive.

  • Actually I wasn't sure about the English term though and yes, I meant reciprocal assimilation I didn't know the term. well about the case I mentioned /masjed/ has two processes it first becomes /masĉed/ and then the /s/ sound turns into /ĉ/ which gives: /maĉĉed/ There are two processes similar to both gemination and reciprocal assimilation what is the deal with this word?! Mar 8, 2016 at 17:02
  • The original case seems to be progressive voicing assimilation, and regressive POA and MOA assimilation. Mar 10, 2016 at 15:19
  • @sumelic. What do mean by POA and MOA assimilation? Mar 22, 2016 at 22:42
  • 1
    @Adel: Sorry, I should have explained that. POA = point of articulation (the alveolar consonant /s/ is assimilated to the post-alveolar consonant /dʒ/); MOA = manner of articulation (the fricative /s/ is assimilated to the affricate /dʒ/). Mar 22, 2016 at 22:45

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