"An" se utiliza si la proxima palabra comienza con un vocal, mientras que se ulitiza "a" normalmente como "un/una". Ejemplos: 1. On-an: I sat on an arm (Me senté en un brazo) 2. On-a: I sat on a chair (Me senté en una silla) 3. In an: I live in an igloo (Vivo en un iglú) 4. In-a: I live in a big house (Vivo en una casa grande) Espero que esto le ayudará y que no he hecho ningún error :) El español es mi cuarto idioma y mi primera lengua extranjera (Hablo 1. Cebuano, 2. Inglés 3. Filipino) Mi profesora en español es de Chile también. Chao!

"In" and "on" are two prepositions that have many meanings in English. Some basics... "On" is used when something is physically above or atop something else: ex. I set my drink on a table. You use "an" when the next word begins with a vowel sound: ex. I set my drink on an oak table. ex. I set my drink on an oblong table. ex. The bug crawled on an apple. "In" is used to express something inside or surrounded by another thing, like you'd put your tea IN a cup or your groceries IN a bag. ex. I went in a museum yesterday. Again, use "an" when the next word begins with a vowel sound: ex. I went in an amazing store downtown. ex. You shouldn't put a fork in an electric toaster. The /n/ in "an" basically serves as a way to separate the vowel sound of /a/ and the beginning of words that start with vowel sounds. This means a,e,i,o,u....but also sometimes y, or h sounds--ex. He said he would be here in an hour. Remember, it's about the SOUND of the next word, whether it is vowel or consonant, that determines if you use "a" or "an"