Indefinite Articles

1. A

1.1. Identifying function

1.1.1. Pointing out a particular object

1.1.2. The speaker knows the object

1.1.3. The situation makes object definite

1.2. Common noun

2. AN

2.1. Classifying function

2.2. Predicative function

2.3. General Sence

2.4. Idea of singularity