I realise this is likely to be highly theoretical, as in “there could be such sounds but they aren’t phonemic in any language”. But I have a burning curiosity, and I’m hoping that there’s a concrete answer: “they do/could exist, and here’s what they do/would sound like”. (Or, pessimistically, “no, they couldn’t exist”.)
These seem to be the four canonical semivowels, listed everywhere and accepted without controversy:
- [j] corresponds to [i]
- [ɥ] corresponds to [y]
- [ɰ] corresponds to [ɯ]
- [w] corresponds to [u]
All of these are close (or high) vowels. Filling out the close vowels, Wikipedia also suggests these, which are uncited but seem entirely plausible:
- [j̈] corresponds to [ɨ]
- [ẅ] corresponds to [ʉ]
And I’ve seen these other semivowels put forward with corresponding vowels:
- [ʕ] (or [ʕ̞]) corresponds to [ɑ]
- [ɹ] and [ɻ] correspond to “vowels such as [ɚ]”
But I’ve seen one putative semivowel, [ʋ], with no counterpart suggested. Does it need to have a particular vowel counterpart? (I would have thought yes, but I could be wrong.) If not, are there other semivowels without associated vowels?
What vowel (if any) does [ʋ] correspond to? Are the above semivowel–vowel pairs correct? Are there others?
(It occurs to me that syllabic [ɹ̩], [ɻ̍] could be used instead of [ɚ]… in which case [ʋ] might correspond to a syllabic [ʋ̩]. But Wikipedia says that [ɹ̩] is another way to write [ɚ], placing it as a central mid vowel. What kind of vowel would [ʋ̩] be?!)
Conversely, what about the vowels that haven’t been mentioned yet?
- Close vowels across the range have been mentioned. (This makes intuitive sense to me; with the jaw more nearly closed, you can make that not-quite-a-consonant articulation.)
- One mid vowel, [ɚ], has come up. I guess it makes sense that you can still sort-of-articulate with a half-open jaw. So what about the other mid vowels? Is there a semivowel for [e], or [ɛ], or [o]?
- And we have one open vowel in the list, [ɑ]. If you’d told me that open vowels couldn’t have semivowels (no way to sort-of-articulate them), I’d have believed you. Does [ʕ] only happen because it’s pharyngeal, not reliant on the mouth? (In which case, wouldn’t it be the semivowel for all open vowels? Why is [ɑ] special?) What about the other open vowels? Is there a semivowel for [a]?
Reading before asking this:
- Wikipedia, Semivowel (Lists all of the above.)
- Wikipedia, R-colored vowel (Gives [ɹ̩] as equivalent to [ɚ].)
- Eugenio Martínez-Celdrán, Problems in the classification of approximants (Cited by Wikipedia. Lists the canonical semivowels with vowel counterparts. Names [ɹ], [ɻ], and [ʋ] as “closely related to vowels” without specifying which vowels.)
- Carinus, “Is there a vowel equivalent to the bilabial approximant?” (Lists the canonical semivowels, followed by the enigmatic “and so on”. Also adds [ɹ] corresponding to [ɚ].)
- Draconis, answer to “Are semivowels pronounced differently than vowels?” (Lists [w] and [u], [ɥ] and [y], and [ʕ] and [ɑ]. Explains how IPA diacritics could give a range of additional semivowels, but that doesn’t mean they’re all possible or tell me what they’d sound like.)
Not read, because I don’t have access to it: Ladefoged & Maddieson, The Sounds of the World’s Languages (also cited by Wikipedia). If this has the answers to all my questions, please tell me!