Two questions for you wise people: 1) when using the indefinite article with an ancronym that begins /S/, should it be 'an' or 'a' considering that phonetically the acronym would begin with a vowel sound? 2) am I right in thinking that generally with words beginning with /h/, 'an' is used when that /h/ is silent such as in "I'll be there in an hour", and that 'a' is used when the /h/ is voiced such as in "I saw a horrible beast"? (In accents that drop /h/ such as cockney, the 'an' form would be seen more prevelantly of course) p.s. there are other examples on which I'm clearer such as with words that begin with an orthographic vowel but have a phonetic, intial consonant sound such as 'user'. Question 2 becomes more difficult with the pronounciation of 'a' in so much as the variant schwa sound vs the more definite dipthong /eI/. I just wish the correct way generally to approach the subject.