Modals: can, could, would, should, might, may, must, will, shall, have to, needs to, had better, and ought to.
| Functions | Modals | Examples |
| possibility | must, will/would, should, may, can/could, might | I might try riding a unicycle. |
| ability | can, could | I can ride a unicycle. |
| necessity | must, have to, should | I must try riding a unicycle while I'm here. |
| permission | may, could, can | Can I try your unicycle? |
Examples:
You should make more of an effort in your studies. (advice)
You should have made more of an effort in your studies. (past)
He said that he
might come if he can get out of work early.
(possibility)
He said that he
might have come if he
could have gotten out of work early. (past)
Jerry would
go to Hawaii if he had some vacation time. (conditional)
Jerry would have gone to Hawaii if he had had some vacation
time. (past)
Susan had better
start arriving on time if she wants to keep her job. (warn)
Susan needs to work harder if she wants to pass the course. (necessity)
If he
missed the meeting, he must have been very sick. (certainty;
past)
Modals: must, have to
Rule 1: We use
MUST to
express personal feelings about having to do something.
Example 1: I
must call
Uncle John this weekend to see
how he's doing.
Example 2: Republicans
must give
up something if there is ever going to be an agreement on
debt reduction.
Rule 2: We use
HAVE TO
to express facts.
Example 1: Unfortunately, I'm
going to miss the party. I
have to finish this report before
tomorrow.
Example 2:
He
has to wear safety glasses
while welding.
Rule 3: We use
MUST to
talk about present and future actions.
Example:
They must get organized if they want this business to
succeed.
Negative
Forms
Rule 4:
MUST NOT and
DO NOT HAVE TO
have different meanings.
Example 1: He
must not take this medication
before driving. = For his safety,
he cannot take this
medication before driving.
Example 2: He
doesn't have to take the early
train. Let's make it for eleven in the morning. =
It is
not necessary to leave
that early because the meeting will be later in the morning.