Relative clauses and non-finite clauses

This will be a brief explanation about relative clauses and non-finite clauses.

Defining:  Is an essential part of the sentence.

There were four students who missed class at 7 a.m.

He is the teacher whose wife just died.

Non-defining: Is extra information, always separated by commas and the speech changes.

The class, which was missed by four students, started at 7 a.m.

The teacher’s wife, who just died, always made pie for students.

Which

Is used to introduce a non-defining clause:
The train, which was late, exploded.

Always follow a preposition:

It was a help for which I’ll be eternally grateful.

That

Is more informal than which:
By 4:30, there was only one painting that hadn’t been sold.

Is often used instead of who in everyday speech in defining clauses:
Do you know the girl that lives next door?

Whom

Whom is the object form of who.
He was a person whom everyone regarded as trustworthy.

Whom is always followed by preposition:

With whom were you dancing?

However, in everyday use, it is usual avoid this kind of construction:

Who were you dancing wih?

Whose

Whose means “of whom”. Can be used in both defining and non-defining clauses:

Several guests, whose cars were parked outside, were waiting at the door.
Several guests whose rooms had been broken into complained to the manager.

When and Where

Non-defining: They follow a named time or place.

Come back at 3:30, when  I won’t be so busy.
I stopped in Maidstone, where my sister owns a shop.

Defining:  When follows words such as time, day, moment.

There’s hardly a moment when I don’t think of you.

Where follows words such as place, house, street.

This is the street where I live.

Non-finite clauses containing an –ing form

These are clauses without a main verb.

Actions happening at the same time:
Waving their scarves and shouting, the fans ran onto the pitch.

One action before another:

Opening the letter, she found that it contained a cheque of $1,000.

An event which is the result of another event:
I didn’t get wet, having remembered to take my umbrella.