Rules of indefinite articles. 1. 'A' is used before a consonant: Example: a dog, a cat, a pen, a table 2. 'An' is used before a vowel. Example: an animal, an orange, an article, an apple, an umbrella. 3. If the pronunciation of vowel comes before the pronunciation of the consonant used, 'An' is used. Example: An MLA / SDO / SDM / M.Sc. / hour 4. If the vowel is pronounced as 'U' or 'Oa' (as in 'one') Example: A one-rupee note / one-act play / university / union / European. 5. If the pronunciation of 'h' is silent, 'an' is used. Example: An hour / honourable man / honest man. 6. An indefinite article is used before a proper noun to refer to an indefinite person. Example: A Mr. Das has come. (=A person named Mr. Das has come) 7. An indefinite article is used before a proper noun to refer to compare a person with another great person. Example: You are a Kalidas, I see. (= Your poetic skill is like that of Kalidas...