Infinitive

The infinitive is a verb form. It has no person, number, mood, or tense.

 The infinitive in English 
In English, there are two main forms of the infinitive:

 the full infinitive (to-infinitive) has the word to at the beginning. For example: I want to run 
 the bare infinitive does not have the word to. For example: I must go.

After a modal verb you must use an infinitive. For example, I must go, he must go (he must goes is not correct)

To express time relationships, here are 8 types of infinitives:

 simple infinitive, for example, to write
 continuous infinitive, for example, to be writing
 perfect infinitive, for example, to have written
 perfect continuous infinitive, for example, to have been writing
 passive simple infinitive, for example, to be written
 passive continuous infinitive, for example, to be being writting
 passive perfect infinitive, for example, to have been written
 passive perfect continuous infinitive, for example, to have been being written

 The infinitive in other languages 
 In German, the infinitives end with -en, -eln or -ern. There are 2 exceptions -  (to be) and  (to do). 

In Esperanto, the infinitives end with -i, for example  (to sleep)

 References 

Category:Grammar