Vowel Sounds

   Referring to vowel sounds is not the same as referring to vowel letters. The English language lists five vowel letters -- A, E, I, O and U. And each can be used to represent more than one sound. (Sometimes, Y is included in the list, but technically it's a glide.) For example, the letter 'a' is used to represent several vowel sounds. The vowel in the words 'cat' and 'can' differ, and even these two words can be pronounced differently, depending on dialect and usage. For instance, in the Chicago dialect, the vowel sound in the word 'cat' is pronounced the same as the vowel sound in the word 'can,' the container. Even the word 'can' can differ. Hear it? The first 'can' rhymes with the name, Anne, and the second rhymes with the name, Ken. 
   When I was studying phonetics, one class assignment was to list the number of vowel sounds in my own dialect. I forget the exact number, but it was something like 12 or 15, even though there are only five vowel letters in our 26-letter alphabet. As for the total number of phonemes (specific meaningful sounds), my Northern New Jersey dialect lists something like 36.
   Some dictionaries, the Oxford English Dictionary for example, maintain that 'a' should be used before 'hotel', because the first letter represents what we were told in grade school was an 'aspirate h.' Which is to say it is a kind of blowing out of air (aspirated). This difference shows up in comparing 'hat' and 'at.' The first word starts with an aspiration. 
   I don't agree with the OED on the 'a' before 'historic.' In some dialects, mine included, the 'h' is silent when used in the phrase 'an historic occasion.' But when the word 'historic' stands alone, the 'h' is aspirated.

   Ain't linguistics and phonetics fun? 
   In this editor's opinion, linguistically, all dialects are equal. Each one enables its speakers to communicate quite well within its linguistic community. The only reason some dialects have more prestige than others is because its speakers have more prestige. And that is a social judgment, not linguistic.

   Among hospital and rehab staff we have encountered, there are nurses and techs whose first languages range from Russian to Polish to Spanish to Haitian French to Hindi and Urdu or some of the other languages of the Indian subcontinent. And they all use English to communicate with each other and the patients. So that makes English a lingua franca in this circumstance.