When should "an" be used before a word and when should "a" be used before a word?
I thought that "an" was used before a word beginning with a vowel but I have seen it used in the following way: An MTV production.
You are correct that the article "an" is used with a word that begins with a vowel. You will also see it used with words that begin with a silent "h," such as "honor" and "honest." In older texts, you'll see "an" used with the word "historical," but that usage is considered old-fashioned.
When you see "an" used in such a way as in the example you've given, it's most likely because "an" precedes a vowel sound. For instance, MTV is an acronym, not a word. When we say "MTV," we sound out each letter, and the letter "M" has a vowel sound (we might spell it "em.") If the acronym were TMV, you would write "A TMV production" because the letter "T" does not have a vowel sound. Or if we were to replace the acronym with the words it represents, we'd write "a Music Television production."
I hope this makes sense to you. Here's what a style guide has to say:
Most of the confusion with a or an arises from acronyms and other abbreviations: some people think it's wrong to use an in front of an abbreviation like "MRI" because "an" can only go before vowels. Not so: the sound, not the letter, is what matters. Because you pronounce it "em ar eye," it's "an MRI."
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The answers below are great, detailed answers. I just wanted to back those up by saying that the use of "a" and "an" can be a confusing skill to master. Basically, you must say the word and hear how it sounds with the articles before it. Most times, you will hear one article sounds correct. I am calling "a" and "an" articles. Articles are considered adjectives (just an extra tidbit).
"A" comes before a word beginning with a consonant.
"An" comes before a word beginning with a vowel.
There are a few exceptions. If the beginning of a word or acronym sounds like a vowel, then the use of "an" is the better choice.
an empty jar
an MTV program (This is what you were questioning. The "M" in MTV sounds like "em". Therefore, you would use "an" just as you would before a word beginning with a vowel.)
I am an elementary school teacher. I speak on a simple level. Hope this was helpful. But as I said before, the answers below are wonderful, detailed answers.
You honestly have to listen to what you are saying/writing. It is mostly executed based on phonetic sound. MTV has the first letter as "M". It SOUNDS like "emcee, eminem, enema". When it comes to letters, you go with how you think you would spell it: M = EM (at least that is how I would spell it if I had to). Since I would spell the letter beginning with an "E", I would use an "an". The sound will tip you off every time. If it is a little awkward to say, then it is probably wrong. You wouldn't say "a hour, an opossum (my fave), an hug". But there are some definitive rules that can help that I teach my students:
"A" goes before consonants such as "cat, dog, fish".
-But- you put an "An" before an "h" that does not carry a sound(meaning you hear the sound of the vowel behind it) such as "hour, honor" not "high, home"
"An" goes before vowel such as "orange, apple, emu"
-But- you put an "A" in front of words that start with "u" but have a "y" sound like in the word "you" or an "o" that have a "w" sound like in the word "won" such as "union, usurper, unicorn" and "one"
Bear in mind that an is used before singular nouns starting with a vowel sound . Some letters look "vowels" but they don't sound "vowels". Example: "u" in university......Actually we say a university not an university.
Therefore, the letter M is pronounced with the sound "e" at the beginning. Then we need to use an before it.
To sum up, sound (what we say) not letter (what we write) is what controls the issue.