To construct an adjective clause, of course, we need to elements, they are : Main clause and sub clause. Besidesm we need a conjunction to link or to combine both of clauses. This linker is called "Conjunctive Pronoun".
There are four kinds of conjunctive pronoun in Adjective Clause, they are:
How to Use The Conjunctive Pronoun
When the subject of a main clause is needed to be a focus of speaking or we would like to add some information about the subject then the conjunctive pronoun /who/ must be used.
Lina : the director rejected the proposal.
Wita : Who does the director work for?
Lina : He works for PT.Andalas.
Wita's question appears when she doesn't know who the director works for. We can say that Lina doesn't give information about the director. On the other hand, Lina just tells wita that their proposal had been rejected by the director.
A New information for the subject is /he works for PT.Andalas/. Take notice that the word 'he' indicates 'the director'.
So, there are two sentences (two main sentences) and both of them must be combined to construct an adjective clause. The two sentences are:
1. The director rejected the proposal.
2. He (or the director) works for PT.Andalas.
Here's how to combine them!
The director who works for PT.Andalas rejected the proposal.
In the example above, the sentence /he works for PT.Andalas/ turns into Sub clause. Because the word /he/ has been changed into the conjunctive pronoun /who/.
We also can say that a conjunctive pronoun /who/ substitute the subject /he/. Because /he/ represents the subject /the director/.
Whom is used to ask about Object. Or, the focus of Discussion is in the Object.
Linda shows me the secret.
I met her yesterday.
When the two sentences are combined, the sentence or the adjective clause will be like this:
Linda whom I met yesterday shows me the secret.
The sentence 'Whom I met yesterday, asking about the object of the sentence.
Study this follows!
I met her yesterday,
I met her yesterday
/whom I met yesterday/ is a sub clause. Take notice that a Conjunctive Pronoun /Whom/ Subsitute the object.
When the subject tells about a things, then the conjunctive pronoun /which/ is used.
1. The book is on the table.
2. The book is expensive.
Both sentences are the same focus, that is, /the book/.
Because the two sentences have the same subject, and /the book/ is /subject/ then one of the Subject must be omitted.
Study this folows!
The book which is on the table is expensive.
When you would like to express possession then the conjunctive pronoun /whose/ is used.
1. The author likes writing a short story.
2. The book is new.
The author whose book is new likes writing a short story.
Besides, we can use /THAT/ as well as /who/, /whom/ and /which/.
The book that is on the table is expensive.
Linda that I met yesterday shows me the secret, etc
which => that
whom => that