Articles a/an

1. In English, the indefinite article is used in both its forms "a" and "an" to refer to singular rouns

2. "A" is used for singular nouns, and "An" is used for singular nouns if begin with a vowel

3. Example of the use of "A": This a Book.

3.1. Some words may be written starting with a vowel, but pronounced with initial consonant sounds. like words beginning with y, u, o

3.1.1. Example: "A Union" or "A one-legged man"

4. Example of the use of "An": This is an Alarm clock.

4.1. Some words can be written beginning with a consonant, but are pronounced with initial vowel sound as words starting in "H"

4.1.1. Example: an hour, an honest error.