1. In English, the two indefinite articles are a and an. Like other articles, indefinite articles are invariable. You use one or the other, depending on the first letter of the word following the article, for pronunciation reasons
2. video
3. article an
3.1. Use an when the next word starts with a vowel (a,e,i,o,u) or with a mute h.
3.2. EXAMPLES
3.3. 1-AN ILLNESS
3.4. 2-AN OBSTACLE
3.5. 3-AN UNIT
4. article a
4.1. Use a when the next word starts with a consonant, or before words starting in u and eu when they sound like you.
