What is a Definite Article and an Indefinite Article explains the grammatical significance of definite articles and indefinite articles.
Definite Articles and Indefinite Articles
1. Articles are Adjectives
A, an, and the are articles and they belong to the adjective family. Articles act like adjectives because they point to nouns.
2. Articles Modify Nouns
The is referred to as the definite article because it limits the meaning to one specific person, place or thing and to no other.
A and an are referred to as indefinite articles because they do not limit the meaning to one specific person, place or thing.
3. Articles are Essential and Non-essential
Use the definite article the with that to convey an idea essential to meaning. The book that…
Use indefinite articles a and an with which to convey an idea that is non-essential to meaning. A book which…
The indefinite articles a and an have the same meaning. Which to use is determined by the pronunciation of the word that follows.
The initial sound of a word (not its spelling) determines whether to use a or an.
An is used before all vowel sounds except the sound of u (a unit, a university or a united front).
An precedes abbreviations that begin with a vowel sound, numbers that begin with a vowel sound and words that begin with a silent h sound (an honest man or an hour).
Articles That Precede Adjectives
When two or more adjectives describe the same noun, us the article before the first adjective.
When two or more adjectives describe different nouns, use the article before each adjective.
Articles That Precede Nouns
When nouns seem to form a single whole, place the article before the first noun only.
When the nouns refer to different persons or things, place the article before each noun.
Sometimes the indefinite article is used incorrectly before a noun especially when the word kind is used.
What kind of a man is he? (incorrect)
What kind of man is he? (correct)
Resources For What is a Definite Article and an Indefinite Article
English Grammar in Use by Raymond Murphy
Plain English Handbook by J. Martyn Walsh and Anna Kathleen Walsh
The Only Grammar Book by Susan Thurman
Mastering English Grammar by S.H. Burton