English language is delicate just like any other languages. Even the native speakers do error here and there. Some of the mistake people do especially from non-native speakers is not able to determine the right application of Determiner (A, An, The).

In this guide will see what determines the application of determiner but first let understand what Determiner is in English language?
What is Determiner in English Language?
A determiner is a word that determines the referent of a noun (subject or object). In other words, a determiner is a word that precedes a noun and says which we’re talking about and which is which on a set of similar nouns.
What determines an application of determiner is simply the sound of a word of “Noun” or “Adjective” following a Determiner (NOT the spelling!), and must be of a new paragraph.
Application of Determiner A, An & The
An: use indefinitely (general) Article “an” Determiner when starting a new paragraph, where a singular noun or adjective word following the determiner begins with a vowel sounds (a,e,i,o,u).
A: use indefinite (general) Article "a'' when starting a new paragraph, where a singular noun or adjective word following the determiner begins with Consonant sounds (b,c,d,f,g,h,j,k,l,m,n,p,q,r,s,t,v,w,x,y,z).
The: use definite (specified) determiner “the” when singular noun or adjective word that come after the determiner has been mentioned or known in the same paragraph.
The: use definite (specified) article '‘the’' when referring to a particular singular noun among its similar nouns, and use before a noun phrase.
Application of Demonstrative Determiners
Basically, the Demonstrative Determiner this, these, that & those are use in pointing out a noun or adjective that has been mentioned or known, and you don’t want to mention it again.
This: use in a singular noun or adjective in closer ange.
That: use in a singular a noun or adjective in far range.
These: use in a plural noun or adjective in closed range.
Those: use in a plural noun or adjective in far range.
Application of Qualifiers as Determiner
Use qualifiers As, Few, Many, Such before any noun, pronoun, adjective, plural noun and collective noun. No other Determiners should come before those qualifiers. e.g.
Few rich people were bad. (Correct)✔
Many actors were also musicians.(Correct)✔
A Such bad boys (Wrong)❌
An as a good teacher…(Wrong)❌
Application of Possessive Determiner
Use My, Your, His, Her, Its, Our, Their before singular/plural noun or adjective and should replace any other Determiner before the noun or adjective. e.g.
Her car.(Correct)✔
Her a car.(wrong) ❌
A Her car. (wrong) ❌
Our nice car. (Correct)✔
An Our nice care.(Wrong)❌
Our an aeroplane. (Wrong)❌
.
Your book. (Correct)✔
The Your* book. (Wrong)❌
Your the book. (Wrong)❌
When Not to Apply Determiner
Don’t use Determiners (“a”, “an” or “the”) when followed by a plural noun, collective noun or pronoun. e.g.
Abu and Jinnie..(correct)✔
An Aladdin and Jinnie…(Wrong)❌
They are coming.(Correct)✔
A they are coming. (Wrong)❌
Men have..(Correct)✔
A Men have (Wrong)❌
Crew of men (correct)✔
A Crew of men (incorrect)❌
No determined for a single proper noun (specified noun) or a single relative pronoun (specified pronoun). But if there are two proper nouns or two relative pronouns of same name being mentioned and you want to mention one not the other, use Article “The”. Additionally, in use of proper noun in a sentence, the first letter of every proper noun must be upper case. e.g.
Disney land (correct if the Proper noun “Disney land” is only one with the name (Unique). In this case A/An/The Disney land is Wrong.
“The Disney land” in America,..(correct if there are more than one proper nouns with the name “Disney land” mentioned, and you want to specify one over the other. In this case, you specified the proper noun with the Article "“The**”.)
Hope this is helpful?
Practice, practice and practice to perfect your use of Determiners.
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