The infinitive is the base form of a verb. Present infinitive is the most common. There are four other forms of the infinitive.
Perfect continuous infinitive
The present infinitive has two forms:
* the to-infinitive=to+base. To sit, to eat, to have
* the zero infinitive=base. Sit, eat, have
The negative infinitive is formed by putting not:
I decided not to go to London.
The to-infinitive is used in many sentence constructions, often expressing the purpose of something or someone’s opinion about something.
THE functions of infinitive
1. As the subject, it is usually placed after the predicate and the sentence is introduced by the introductory it.
It is very hard to work under such conditions.
2. Can be used as a part of the Compound Predicate.
The plane was to go the director
3. As an object.
I hate to ask people such questions.
4. Can be used as an attribute.
THE captain was the last to leave the ship.
In negative form it takes not before infinitive.