Use: We usually use MUST and HAVE TO interchangeably to say that it is necessary to do something. Sometimes, we must use one or the other.
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. Usually, "outside" forces make things
necessary.
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.
