N. V. Tatsenko introduction to theoretical phonetics of english

[n] as in spot and wasp. This vowel is not quite back, and between open-mid and open in tongue height. The lips are slighdy rounded.
[u] as in put and full. The nearest cardinal vowel is No. 8 [u], but it can be seen that [u] is more open and nearer to central. The lips are rounded.
M as in water and banana. This central vowel - which is called schwa - is a very familiar sound in English; it is heard in the first syllable of the words 'about', 'oppose', 'perhaps', for example. It is different from the other vowels and needs separate consideration.
Schwa is the most frequently occurring vowel in English, which is always associated with weak syllables. In quality it is mid (i. e. halfway between close and open) and central (i. e. halfway between front and back). It is generally described as lax - that is, not articulated with much energy. Of course, the quality of this vowel is not always the same, but the variation is not important. Not all weak syllables contain [э], though many do. Learners of English need to learn where [э] is appropriate and where it is not. To do this we often have to use information
that traditional phonemic theory would not accept as relevant - we must consider spelling. The question to ask is: if the speaker were to pronounce a particular weak syllable as if it were strong instead, which vowel would it be most likely to have, according to the usual rules of English spelling? Knowing this will not tell us which syllables in a word or utterance should be weak but it will give us a rough guide to the correct pronunciation of weak syllables. Let us look at some examples:

1. 
   spelt with 'a'; strong pronunciation would have [ж]
   

'attend' [atennd] 'character' [ksrakta] 'barracks' [bsraks];

2. 
   spelt with 'ar'; strong pronunciation would have [o:] 'particular' [patikjala] 'molar' [maola] 'monarchy' monaki];
   
3. 
   adjectival endings spelt 'ate'; strong pronunciation would have [ei]:
   

'intimate' [intimat] 'accurate' [skjarat] 'desolate'
[desalat] (although there are exceptions to this: 'private' is usually praivit]);

4. 
   spelt with 'o'; strong pronunciation would have [o] or [au] 'tomorrow' [tamorau] 'potato' [pateitau] 'carrot' [ksrat];
   
5. 
   spelt with 'or'; strong pronunciation would have [o:] 'forget' [faget] 'ambassador' [smbssada]
   

'opportunity' [opatjuniti];

6. 
   spelt with 'e'; strong pronunciation would have [e] 'settlement' [setlmant] 'violet' [vaialat] postmen' [paostman];
   
7. 
   spelt with 'er'; strong pronunciation would have [з:] 'perhaps' [pahsps] 'stronger' [stroqga]
   

'superman' [su:pamsn];

8. 
   spelt with 'u'; strong pronunciation would have [л] 'autumn' [o:tam] 'support' [sapo:t] 'halibut' [hslibat];
   
9. 
   spelt with 'ough' (there are many pronunciations for the letter-sequence 'ough')
   

'thorough' [9лге] 'borough' [Ьлш];

10. 
    spelt with 'ou'; strong pronunciation might have [au]
    

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