Forming the infinitive

The infinitive is the base form of a verb. In English, when we talk about the infinitive we are usually referring to the present infinitive, which is the most common. There are, however, four other forms of the infinititive: the perfect infinitive, the perfect continuous infinitive, the continuous infinitive, & the passive infinitive.

The present infinitive has two forms:

  • the to-infinitive = to + base
  • the zero infinitive = base

The present infinitive base is the verb form you will find in a dictionary.

To-infinitive Zero infinitive
to sit sit
to eat eat
to have have
to remember remember

The negative infinitive is formed by putting not in front of any form of the infinitive.

  • I decided not to go to London.
  • He asked me not to be late.
  • I'd like you not to sing so loudly.
  • I'd rather not eat meat.
  • I might not come.

Functions of the to-infinitive

The to-infinitive is used in many sentence constructions, often expressing the purpose of something or someone's opinion about something. The to-infinitive is used following a large collection of different verbs as well. See this page about verbs followed by infinitives.

The to-infinitive to indicate the purpose or intention of an action

In this case to has the same meaning as in order to or so as to.

  • She came to collect her pay cheque.
  • The three bears went to find firewood.
  • I am calling to ask you about dad.
  • You sister has gone to finish her homework.
The to-infinitive as the subject of the sentence

This is a formal usage and is far more common in written English than spoken

  • To be or not to be, that is the question.
  • To know her is to love her.
  • To visit the Grand Canyon is my life-long dream.
  • To understand statistics, that is our aim.
The to-infinitive to indicate what something can or will be used for

In this pattern, the to-infinitive follows a noun or pronoun.

  • The children need a garden to play in.
  • I would like a sandwich to eat.
  • I don't have anything to wear.
  • Would you like something to drink?
The to-infinitive after adjectives

There is a common pattern using the to-infinitive with an adjective. These phrases are formed:
subject + to be + adjective + (for/of someone) + to-infinitive + (rest of sentence)

Subject + to be + adjective (+ for/of someone) + to-infinitive (+ rest of sentence)
It is good   to talk.  
It is good of you to talk to me.
It is important   to be patient.  
It is important for Jake to be patient with his little brother.
I am happy   to be here.
The dog is naughty   to destroy our couch.
The to-infinitive to make a comment or judgement

To use the to-infinitive when making a comment or judgement about a noun, the pattern is:
Subject + to be + noun phrase + to-infinitive

Subject + to be + noun phrase + to-infinitive
It was a stupid place to park.
That is a dangerous way to behave.
What you said was a rude thing to say.
This is the right thing to do.
Those were the wrong kind of eggs to buy.
Jim is the best person to hire.
The to-infinitive with adverbs

The to-infinitive is used frequently with the adverbs too and enough to express the reasoning behind our satisfaction or insatisfaction. The pattern is that too and enough are placed before or after the adjective, adverb, or noun that they modify in the same way they would be without the to-infinitive. We then follow them by the to-infinitive to explain the reason why the quantity is excessive, sufficient, or insufficient. Normally the to-infinitive and everything that follows can be removed, leaving a sentence that still functions grammatically.

  • There's too much sugar to put in this bowl.
  • I had too many books to carry.
  • This soup is too hot to eat.
  • She was too tired to work.
  • He arrived too late to see the actors.
  • I've had enough food to eat.
  • She's old enough to make up her own mind.
  • There isn't enough snow to ski on.
  • You're not old enough to have grand-children!
The to-infinitive with question words

The verbs ask, decide, explain, forget, know, show, tell, & understand can be followed by a question word such as where, how, what, who, & when + the to-infinitive.

  • She asked me how to use the washing machine.
  • Do you understand what to do?
  • Tell me when to press the button.
  • I've forgotten where to put this little screw.
  • I'm not sure I know who to call.

Functions of the zero infinitive

The zero infinitive after auxiliaries
  • She can't speak to you.
  • He should give her some money.
  • Shall I talk to him?
  • Would you like a cup of coffee?
  • I might stay another night in the hotel.
  • They must leave before 10.00 a.m.
The zero infinitive after verbs of perception

With verbs of perception, the pattern is verb + object + zero infinitive.

  • He saw her fall from the cliff.
  • We heard them close the door.
  • They saw us walk toward the lake.
  • She felt the spider crawl up her leg.
The zero infinitive after the verbs 'make' and 'let'
  • Her parents let her stay out late.
  • Let's go to the cinema tonight.
  • You made me come with you.
  • Don't make me study that boring grammar book!
The zero infinitive after the expression 'had better'
  • We had better take some warm clothing.
  • She had better ask him not to come.
  • We had better reserve a room in the hotel.
  • You'd better give me your address.
  • They had better work harder on their homework.
The zero infinitive with "why"

The question word why is followed by the zero infinitive when making suggestions.

  • Why wait until tomorrow?
  • Why not ask him now?
  • Why leave before the end of the game?
  • Why walk when we can go in the car?
  • Why not buy a new bed?