NFINITIVE
1.THE ZERO INFINITIVE WITH "WHY"
The question word why is followed by the zero infinitive when making suggestions. EXAMPLES
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? Examples
with 'to'

The elephant decided to marry the mouse
The mouse agreed to marry the elephant
You will have to ask her
You are to leave immediately
He ought to relax
She has to go to Berlin next week
It's easy to speak English
It is hard to change jobs after twenty years
It's stupid to believe everything you hear
without 'to'

I would rather visit Rome. She would rather live in Italy. Would you rather eat steak or fish? He would rather work in a bank. I'd rather be a forest than a tree. THE ZERO INFINITIVE
The zero infinitive is used:
after most auxiliaries (e.g. must, can, should, may, might)
after verbs of perception, (e.g. see, hear, feel) with the pattern verb + object + zero infinitive
after the verbs 'make' and 'let', with the pattern make/let + object + zero infinitive
after the expression 'had better'
after the expression 'would rather' when referring to the speaker's own actions
Examples
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.
After verbs of perception:
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. After the verbs "make" and "let":
Her parents let her stay out late.e.g. want, wish, agree, fail, mean, decide, learn
After the auxiliaries to be to, to have to, & ought to
In the pattern 'it is + adjective + to-infinitive'
FUNCTIONS OF THE ZERO INFINITIVE
THE ZERO INFINITIVE AFTER AUXILIARIES
EXAMPLES
She can't speak to you.THE ZERO INFINITIVE AFTER THE VERBS 'MAKE' AND 'LET'
EXAMPLES
Her parents let her stay out late.2.Shall I talk to him?