The most common uses of the infinitive are:

To indicate the purpose or intention of an action (where the ‘to’ has the same meaning as ‘in order to’ or ‘so as to’):

  • She’s gone to collect her pay cheque.
  • The three bears went into the forest to find firewood.

As the subject of the sentence:

  • To be or not to be, that is the question.
  • To know her is to love her.
    (Note: this is more common in written English than spoken)

With nouns or pronouns, to indicate what something can be used for, or what is to be done with it:

  • Would you like something to drink?
  • I haven’t anything to wear.
  • The children need a garden to play in.

After adjectives in these patterns:

  • It is + adjective +to-infinitive
    It is good to talk
  • It is + adjective + infinitive + for someone + to-infinitive.
    It is hard for elephants to see mice
  • It is + adjective + infintive + of someone + to-infinitive.
    It is unkind of her to say that.

After an adjective + noun when a comment or judgement is being made:

  • It was a stupid place to park the car.
  • This is the right thing to do.
  • It was an astonishing way to behave.

With too and enough in these patterns:

too much/many (+ noun) + to-infinitive

  • There’s too much sugar to put in this bowl.
  • I had too many books to carry.

too + adjective + to-infinitive

  • This soup is too hot to eat.
  • She was too tired to work.

too + adverb + to-infinitive

  • He arrived too late to see the actors.

enough (+ noun) + to-infinitive

  • I’ve had enough (food) to eat.

adjective + enough + to-infinitive

  • She’s old enough to make up her own mind.

not enough (+noun) + to-infinitive

  • There isn’t enough snow to ski on.

not + adjective + enough + to-infinitive

  • You’re not old enough to have grand-children!