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 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:

make	She made Peggy and Samantha clean the room.

หลักการใช้ Infinitive without to

       1. ตามหลัง Helping verb (Auxiliary verb) ยกเว้น be, have, ought, used เช่น

                Don’t mention it.

          You must drive on the left side.

     2. ตามหลัง had better, would rather, rather than, but

                You’d better see the doctor.

          She’d rather watch TV. than listen to the radio.

     3. หลัง กริยาต่อไปนี้ have [somebody do something], please, help, let,make    

  ใน active voice

          They let the thief escape.           [Active]

          The thief was let escape.           [Passive]

      4. หลัง กริยาต่อไปนี้ จะตามด้วย inf. Without to หรือ present participle [V.ing]

          See              watch          notice          observe       hear

          Smell           feel

          I heard your phone ring last night.       [a complete action]

          I heard your phone ringing last night.   [continuous action]

หมายเหตุ:

Infinitive without "to" หน้าตาเหมือนv.1 

  แต่ไม่มีการเติม s, es นะจ๊ะ 

-  Modal Verb + V.inf

Modal Verb : can, could, shall, should, will, would, may, might

-  Causative Verb + V.inf

Causative Verb : Have/Make/Let  someone do something

แต่ถ้าเป็น Get หล่ะ จะใช้ยังไง Get ต้อง someone to do something เลย

-     Have / Get + something done

ที่ทา : http://www.dek-eng.com/2453/Special-Interviews/Infinitives/Infinitive-with-and-without-to.html