The adjective clause is used in the same way as the adjective. According to English grammar, an adjective modifies or adds information to a noun. Similarly, an adjective clause modifies or adds information to a noun.
To distinguish, an adjective is simply a word, whereas an adjective clause is a dependent clause, but both perform the same function, which is to modify or identify a noun.
Furthermore, English grammarians have clarified that an adjective clause starts right after a noun and not before any other parts of speech. Second, they’ve clarified that it comes after the noun it modifies.
To illustrate, Ali likes Karachi, Ali’s brother is a doctor. If we combine the aforementioned sentences into a complex sentence (a combination of a dependent and an independent clause), then Ali whose brother is a doctor likes Karachi. The complex sentence below will be incorrect according to grammar. Ali likes Karachi whose brother is a doctor.
As a result, English grammar states that the adjective clause must come after the noun about which you are providing information. Here we can see that our information is about Ali rather than Karachi. The adjective clause should then begin after the noun ‘Ali,’ not Karachi.
Furthermore, Balochistan is beautiful. I live in it. In a complex sentence, it will be Balochistan, where I live, is beautiful. Below one is wrong, Balochistan is beautiful where I live. Even though the sense is correct, grammar states that adjective clauses cannot come after other parts of speech. Here we can see the adjective clause starts after ‘beautiful’ and beautiful is an adjective. Even when they make complete sense, grammar errors cause them to be incorrect.
More specifically, adjective clauses are divided into two types: defining adjective clauses and undefining adjective clauses.
A defining adjective clause defines a noun, whereas an undefining adjective clause provides additional information about the noun. Because it has already been identified.
Inverted commas are always used to separate undefining adjective clauses. Because Balochistan has already been identified, ‘where I live’ is an additional piece of information. That’s why it’s surrounded by inverted commas.
In addition, the adjective clause is also known as relative clause, defining clause, modifying clause, essential clause, and identifying clause in some books. However, it is more commonly known as a relative clause or an adjective clause. It is referred to as a relative clause because it begins with relative pronouns, and it is referred to as an adjective clause because it functions as an adjective.
According to one of the most well-known and international English grammar books, Wren & Martian, it is an adjective clause. To summarize, it is fully explained on page 165 of the Wren & Martian High School English Grammar & Composition book, along with numerous exercises.