An is used in front of words which begin with 'h' when the letter is silent. e.g. an hour A is used in front of vowels when the vowel is pronounced as a consonant. e.g. a university (u is said as y) A or an is used based on the following sound, not the following letter.

In English, the indefinite articles "a" and "an" are used before singular nouns. "A" is used before nouns that start with a consonant sound, and "an" is used before nouns that start with a vowel sound. For example, we would say "a car" because the word "car" starts with a consonant sound. We would say "an apple" because the word "apple" starts with a vowel sound. There are a few exceptions to this rule. One exception is when the noun starts with the sound "h". If the "h" is silent, then we use "an" instead of "a". For example, we would say "an hour" because the "h" in "hour" is silent. Another exception is when the noun starts with the letter "u". If the "u" is pronounced as a consonant, then we use "a" instead of "an". For example, we would say "a uniform" because the "u" in "uniform" is pronounced as the consonant "y" as in you or yellow. Here are some more examples of when to use "a" or "an": A (consonant sound) a book a table a car a hat a house An (vowel sound) an apple an hour an elephant an umbrella an idea

I don't think 'an horse' is ever proper, except maybe in certain dialects that are not considered standard. For a person of foreign origin, people would just assume it was wrong. It is true there can be much variation in whether an H is pronounced, though I'm not sure there is a much of a difference between Britain and America, even though they differe on individual words, such as herb (Brits say H).

You should all take teacher Claires's advice.

It is always a x -> = a car a bird cat etc or whatever. it is an y -> depends upon the sound of the following first part of the next word. An Horse or an egg an elephant an ostrich an etc. it is never the first letter of the following word but the sound of the first letter in the following word. it's an horse even though the word horse starts with a consonant the sound is an Ho it's a University because university starts with a U sound. A difficult concept to explain but with practice you will soon pick it up.