how should we use the infinitive in grammar

How should we use the infinitive

FUNCTION

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.

webgraphy: http://www.edufind.com/english/grammar/infinitive_function.php