What exactly is the "schwa" sound?

Question

What exactly is the "schwa" sound? As a non-native speaker, I hear this sound as not being a pure and clean sound. I mean I know that every vowel sound may vary depending on whether the syllable is stressed, on the accent of the person that makes the sound, etc. But generally this sound is the same in the sense that it does not depend on the consonant sounds that come before or after, and might or might not be heard as being different by the non-native speaker ear.

The schwa sound is a very difficult one for me because I cannot find a pattern to follow. When I was learning the other vowel sounds I could analyze a long list of words being pronounced (by the same person of course) and then abstract the sound so I can produce it perfectly. But this does not work for the schwa sound. So for example I hear one sound in words like a-bout, b-a-loon, decim-a-l, and a different sound in words like s-u-ppose and impet-u-s, t-o-day or t-o-night. Also in words like Ros-a-'s and ros-e-s, the schwa sounds differently.

When it comes to words that have the schwa sound on vowels e an i like in the word insan-i-ty then the sound is almost the one for the i in t-i-p, but also in words like b-e-hind I hear some people say it with a schwa sound like in a-bout and some other people pronounce it like the i in p-i-t. So, I would really appreciate an explanation about how you perceive this sound and how you would explain it to someone who, like me, is not a native speaker.

Answer 1

First, it's "shwa". It's a Hebrew word, not a German one, so there's no reason for SCH.

Second, it's both a phone [ə] in IPA, and a phoneme /ə/ in English. As a phone, it's got the sound of the final vowel in German Danke, of the first vowel in French Le Mans, or the first vowel in English the man. There is no shwa in Spanish or Italian.

Third, as a phoneme in English, /ə/ doesn't contrast with any other central vowel, so it has a lot of allophones: /ə/ [ɨ] [ə] [ʌ] (in increasing order of stress and decreasing order of speed), plus syllabic resonants [ṃ] [ṇ] [ḷ] [ṛ], before those consonants.

The best way I can suggest to practice the sound [ə] is to open your mouth to say an [e] (whatever that you think that is in your language), and then — while saying it, and without changing how your mouth or lips are positioned — move your tongue backwards toward the center of your mouth.

What you wind up saying is likely to be something close to a shwa.

Answer 2

You have a good ear. In fact, for many speakers, the vowels in "Rosa's" and "roses" are not identical on average. It may be misleading to transcribe them with the same symbol "ə".

You might find the answer I wrote to another question relevant: Exodus word pronounciation - Why it is different from spelling (based on "The phonetics of schwa vowels" by Edward Flemming)

Basically, the realization of what is called the "schwa" varies depending on its position and the surrounding sounds.

When schwa comes before a liquid or nasal such as /l/, /r/, /n/, /m/, the combination is commonly pronounced as a syllabic consonant. Syllabic /l̩/ would be possible (at least in some accents) in "b-a-lloon", and usual in "decim-a-l".

Word-final "schwa" tends to be pronounced with a low-ish vowel quality, phonetically something like [ɐ]. (It may be relevant that in this position it is almost always spelled with the letter "a", and it's basically in complementary distribution with the phoneme /ɑ(ː)/ which doesn't really occur in unstressed open syllables.) This sound may remain the same even when suffixes like "-s" or "-'s" are added, so many speakers use something like [ɐz] at the end of "commas" or "Rosa's". In non-rhotic British English, this is the same sound that occurs at the end of the word "lett-er".

In the middle of a word, schwa tends to be pronounced with a higher vowel quality, and it assimilates in frontness to nearby sounds. For some accents, it is actually usual practice to distinguish two different kinds of reduced vowels, normally transcribed /ɪ/ and /ə/; and it's /ɪ/ that occurs as the epenthetic vowel before the /z/ of inflectional endings, as in "roses" /roʊzɪz/. Even in accents where schwa is transcribed here, it will often be an /ɪ/-like schwa. Sometimes, to represent this or to represent the possibility of variation between ɪ/ and /ə/, the symbol /ɨ/ or /ᵻ/ is used for the vowel in words like "roses".

Adjacent labial consonants like /b/ and /m/ would tend to contribute to a "back-er" pronunciation of schwa (closer to /ʊ/ or /ʌ/), while adjacent coronal consonants such as /s/ and /t/ would tend to contribute to a fronter pronunciation of schwa (closer to /ɪ/) in s-u-ppose, impet-u-s, t-o-day or t-o-night.

Another relevant factor is voicing. Any vowel in English will be pronounced with shorter duration before a voiceless consonant; this includes schwa. When schwa is both preceded and followed by a voiceless consonant, as in "suppose", it may be devoiced.