Relatively Speaking

Relative Clauses are clauses are phrases that describe the nouns they are attached to. In an earlier post, we discussed relative pronouns (who, whose, which, where, when and that), which we use to attach two separate sentences. There are two types of relative clauses: defining and non-defining.

A defining clause describes the noun it is attached to.

That’s the neighbor. He just got out of jail.

That’s the neighbor, who just got out of jail.

Without defining clause, the sentence doesn’t make too much sense. We add the relative clause to give essential information.

A non-defining clause adds extra information.

The man is an ex-con. He lives next to me.

The man, who lives next to me, is an ex-con.

Without the non-defining clause, the sentence gives sufficient information, but by adding the relative clause, we enrich the sentence.

Now look at the following sentences with relative clauses. See if you can find the difference between them.

I have friends who I have known since my childhood.

I have friends who have known me since my childhood.

In the first sentence, we have a subject after the relative pronoun, but not in the second sentence.

The relative clause can only have a subject if it is different from the noun before the relative pronoun. For example we cannot say:

I have friends who they have known me since my childhood.

because the subject (they) is the same as the object (friends). 
But we can say: 
I have friends who I have known since my childhood.
because the subject (I) is different from the object (friends). 
In the same way, you can't have an object in the relative clause if it's the same as the noun before the relative pronoun. 
So we cannot say:
I have friends who I have known them since my childhood. 

On the other hand, we do not need a relative pronoun if we have a subject in the relative clause:

I have friends ___ I have known since my childhood.

But we cannot omit the relative pronoun when there is no subject in the relative clause, otherwise it the sentence won't make sense: 

I have friends ___ have known me since my childhood...
because the noun (friends) cannot be both the object and subject. 
In this case, the relative pronoun acts as the subject:
I have friends who have known me since my childhood.


So as you can see, relative clauses, which add information, make sentences more interesting, don't they?