We use the to-infinitive:
• to express purpose (to answer "Why...?"):
He bought some flowers to give to his wife.
He locked the door to keep everyone out.
We sometimes say in order to or in order not to:
We set off early in order to avoid the traffic.
They spoke quietly in order not to wake the children
… or we can say so as to or so as not to:
We set off early so as to avoid the traffic.
They spoke quietly so as not to wake the children.
• after certain verbs (see verbs followed by infinitive), particularly verbs of thinking and feeling:
choose, decide, expect, forget, hate, hope, intend, learn, like,
love, mean, plan, prefer, remember, want, would like, would love
… and verbs of saying:
agree, promise, refuse
They decided to start a business together.
Remember to turn the lights out.
Some verbs are followed by a direct object and the infinitive(see verbs followed by infinitive):
advise, ask, encourage, invite, order, persuade, remind, tell, warn,
expect, intend, would prefer, want, would like
She reminded me to turn the lights out.
He encouraged his friends to vote for him.
• after certain adjectives.
Sometimes the to-infinitive gives a reason for the adjective:
We were happy to come to the end of our journey
= We were happy because we had come to the end of our journey
John was surprised to see me
= He was surprised because he saw me
Other adjectives with the to-infinitive are:
Unfortunately I was unable to work for over a week.
I am really tired. I’m ready to go to bed.
We often use the to-infinitive with these adjectives after it to give opinions:
It’s easy to play the piano, but it’s very difficult to play well.
He spoke so quickly it was impossible to understand him.
We use the preposition for to show who these adjectives refer to:
It was difficult for us to hear what she was saying.
It is easy for you to criticise other people.
We use the preposition of with other adjectives:
It’s kind of you to help.
It would be silly of him to spend all his money.
• As a postmodifier (see noun phrases) after abstract nouns like:
I have no desire to be rich.
They gave him an opportunity to escape.
She was annoyed by her failure to answer the question correctly.
• We often use a to-infinitive as a postmodifier after an indefinite pronoun (See indefinite pronouns):
When I am travelling I always take something to read.
I was all alone. I had no one to talk to.
There is hardly anything to do in most of these small towns.