1. Form The infinitive is the base form of a verb. It may be preceded by 'to' (the to-infinitive) or stand alone (the base or zero infinitive).
2. Infinitive with or without 'to'
The to-infinitive is used:
a. after certain verbs. e.g.want, wish, agree, fail, mean, decide, learn b. after the auxiliaries to be to, to have to, and ought to c. in the pattern 'it is + adjective + to-infinitive'