Modal
verbs of obligation :
must,
have to, should and ought
to
There are two types of
modal
verbs of obligation ; those that primarily express a firm
obligation or necessity -
must and
have to
- and those that express a recommendation or moral obligation -
should and
ought
to
Firm obligation,
etc. - must
and have go
The verb
must
only exists
in the simple present and present perfect forms.
While the
present
form can express
obligation,
necessity, certainty
or strong
probability,
the
present perfect
forms
only
express a strongly felt opinion or
supposition.
| All
persons |
Present |
Present perfect |
| Affirmative |
must
|
must have |
| Negative |
must
not, mustn't |
must not have,
mustn't have |
If other tenses are required, the speaker or writer must use forms of
the synonymous modal verb "
have
to" . This modal auxiliary has all normal
tenses, including progressive or continuous forms; these are not
common, but need to be used in some cases.
| Principal
tenses |
Present |
Present
perfect |
Past |
Future |
| Affirmative: |
has
to,
have
to
|
has
had to
have had to |
had
to
|
will
have to |
Negative;
|
does
not have to,
do not have to ,
doesn't have to
don't have to
|
has
not had to
have not had to |
did
not have to
didn't have to * |
will
not have
to
won't have to |
| Progressive or
continuous |
am
having to
is having to,
are having to |
has
been having
to
have been having to |
was
having to
were having to |
will
be having to |
* The form
"had not to"
is sometimes used, but it is generally
considered to be archaic.
Got
to :
In spoken English, and in the present form only, have
to is often substantiated by the word got;
i.e. an alternative to I have
to is I've got
to.
Must and
have to
are used to express :
a. Firm
obligation
or
necessity
b.
Certainty
or strong
probability.
c.
Must have
only :
supposition
Examples:
a1) You
must see a doctor at once !
a2) I have to be at school tomorrow at 8 a.m. I have an
exam !
a21) I've got to be at school tomorrow at .....
a3) You mustn't touch that plate, it's too hot.
a4) I had to see a doctor, because I felt very sick.
a5) I had to break the window ! I lost my key !
a6) The manager isn't here, he's had to go to Paris on urgent
business.
a7) Tomorrow the President will have to open Parliament.
a8) She's having to move because she can't stand the noise.
a9) I'm having to take out this detonator very slowly, to
avoid an explosion.
a10) Oh you're so kind! You didn't have to do it as
well as that !
b1) He must be over eighty, he was born in 1930.
b2) If my brother's not in London, he has to be in New York.
b3) I've got all the right answers, I must be one of the
winners !
b4) If I remember correctly, it has to be here.
c1) I can't find my laptop, I must have left it in the train.
c2) If they're out, they mustn't have heard the news.
Attention
!
Take care to distinguish correctly between "
had to" and
"
must have"
They had to go to London
= They
were obliged to go to London
They
must have gone to London.
= In
my opinion, they have certainly gone to London.
http://linguapress.com/grammar/modal-obligation.htm
