Undefined Articles

1. the noun can be classified according to

1.1. gender

1.1.1. example

1.1.1.1. I have an apple

1.2. or number

1.2.1. example

1.2.1.1. a plane

2. The determined items are

2.1. "a" & "an"

3. basic rules

3.1. When the noun that accompanies the article begins with a consonant, the article "a" is used

3.1.1. consonant

3.1.1.1. example

3.1.1.1.1. a motorcycle

3.2. When the noun that accompanies the article begins with a vowel, the article "an" is used

3.2.1. vocal

3.2.1.1. example

3.2.1.1.1. An elephant

3.3. only "an" or "a" is used when the word that accompanies is sigular

3.3.1. singular