The Infinitive

We can use Infinitive in several ways.

1. We can use the Infinitive as a Subject :

To waste your time is silly.

To succeed needs hard work.

To practise is to become perfect.

To play is good for health.

2. We can use the Infinitive as an Object :

The girls like to dance.

The tutor has started to teach mathematics.

The minister has come to examine the hospital.

The teacher has asked him to tell the truth.

3. We can use the Infinitive as a Complement to Verb :

To save is to earn.

To think is to become wiser.

To play is to enjoy.

It is good for you to work hard.

4. We can use the Infinitive as Object to a Preposition :

The train is about to depart.

The rain is about to start.

5. We can use the Infinitive as Case in Apposition with It as the Subject :

It is silly to put hot food in the fridge.

It is a good idea to start early.

6. With some Verbs, to is not used with the Infinitive; for example : feel, hear, see, let, have, make, notice, watch, bid, dare, need.

For example :

I can see someone knock at the door.

She lets her husband stay out at night.

They felt the floor vibrate.

The people noticed the thief steal a purse.

 7. Some Verbs necessarily take to with the Infinitive; for example : advise, allow, ask, beg, cause, command, compel, enable, expect, get, imagine, induce, instruct, like, order, permit, persuade, require, tell, want, wish; for example :

The watchman allowed him to go in.

The officer caused the work to be done.

The doctor advised him to take medicine on time.

The teacher asked the student to work hard.

8. You may or may not use to with two Verbs : Know and help :

I have known it (to) rain in summer.

Help me (to) cross over the road.

The teacher helped him (to) understand the formula.