Infinitive without to :
after auxiliaries/modals
can
He can run very fast.
could
As a boy he could run very fast.
may
I may fly to Africa this summer.
might
I might fly to Africa this summer.
must
I must go now.
mustn't
You mustn't smoke here.
needn't
You needn't go.
shall
We shall sing a song.
should
We should sing a song.
will
She will cook a meal for his birthday.
would
She would cook a meal for his birthday.
after to do
do
I don't know.
after the following expressions:
had better
You had better clean up your room.
would rather
Susan would rather study for her exam tomorrow.
would sooner
I would sooner read a book than watch this film.
why not
Why not ask your neighbour for help?
why should we
Why should we go by car?
why should we not
Why should we not go by car?
after verbs of perception + object (action has finished):
feel
She feels the rain fall on her face.
hear
I heard Peter sing a song.
notice
Mandy noticed the boy climb the tree.
see
They saw him climb up the roof.
watch
He watched the thieves steal a car.
after let + object:
let
Sandy let her child go out alone.
Mother let her daughter decide on her own.
let's
Let's go for a walk through the park.
after make + object: My mother made me clean my room alone.