Meaning of Key Auxiliary Verbs

A. Will: be willing to; intend to

• I will open the door for you.
• I will be there at 8:00.

B. Shall: intend to (formal); have decided to

• Where shall we sit?
• We shall ask the committee.

C. May / Can: be possible to do

• Can fish live in the river?
• It may rain tomorrow.

D. Can / Could / May: be allowed to do

• May I have one?
• You can take both of them.

E. Must: be necessary; be logically certain
Note: negative = cannot/can't, must not

• This step must be next.
• It must be her purse.

F. Must / Have to: be required to do

• Everyone must be on time.
• They have to work late.

G. Should / Ought to / Had better: be obliged to do

• You should call her.
• We ought to get there early.

H. Should have / Could have + p.p.: was not true; did not happen

• She should have read the book.
• They could have won, but they didn't.

I. Used to / Would: did in the past

• We used to talk every day.
• In the spring, I would plant flowers.