This document discusses different modal verbs used to express obligations, recommendations, assumptions, and deductions in English. It covers must, have to, should, ought to, and had better for obligations and recommendations. It also explains using must, must have, and may/might/could have to make logical deductions and assumptions about the present and past.

1. Modal Verbs
Yasamin - Taghizadeh
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2. Modal verbs of obligation:
Must & Have to :
We can use have to, must express obligation
(something you have to do).
must + infinitive
have to + infinitive
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3. must is often used when
the speaker feels an
obligation himself/
herself
or
we use must when the
speaker feels that
something is necessary.
MUST:(strong obligation)
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 I must study today.
 I must go to the doctor.
 You must exercise . (doctor
says)
 You must be quiet .
(teacher says)

4. Mustn’t is used to
express negative
obligation (an obligation
not to do something )
Or
We use mustn’t to say
that sth is a bad idea .
Mustn’t :
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 You mustn’t drop those
glasses . They’ll break .
 You mustn’t wear your best
clothes . You’ll get them dirty .

5. Must:
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+ : subject + must + verb +….
- : subject +mustn’t+ verb+ ….
? : no used
Must use in present tense but must has
no past tense form , so change to “had
to” (past form of “have to” ).

6. Have to is used when
the speaker feels an
obligation from
outside(a rule , law
, regulation ) or is just
expressing a fact .
Have to :(strong obligation)
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 We have to(have got to) put
the paper to be recycled in the
green box .
 she has to(has got to) buy a
newspaper. The boss asked her to
get one .
* “Have got to” means the same
as “have to” but “have got to” is
in formal . We use it mainly in
the present.

7. Negative form :
“don’t/ doesn’t have to”
means no obligation .
Question form :
Do/ Does +subject +
have to + verb + ….
Negative And Question Form:
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 You don't have to eat
anything you don't like.
 I don't have to work on
Sundays.
 Do I have to do it for
Monday ?
 Does she have to work for
Sunday ?

8. Have to :
*Present :
Have / Has to - don’t/doesn’t have to - do / does
… have to
*Past :
Had to – didn’t have to – did … have to –
*Future :
• For future with “will” only use “will have to”
not Will must
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9. "Should" is most commonly used to make
recommendations or give advice. It can also be used to
express obligation as well as expectation.
Examples:
When you go to Berlin, you should visit the palaces in Potsdam.
recommendation
You should focus more on your family and less on work. advice
I really should be in the office by 7:00 AM. obligation
By now, they should already be in Dubai. expectation
Advice And Recommendation :
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10. "Ought to" is used to advise or make recommendations. "Ought to"
also expresses assumption or expectation as well as strong probability,
often with the idea that something is deserved. "Ought not" (without
"to") is used to advise against doing something, although Americans
prefer the less formal forms "should not" or "had better not.“
Examples:
You ought to stop smoking. recommendation
Jim ought to get the promotion. It is expected because he deserves it.
This stock ought to increase in value. probability
Mark ought not drink so much. advice against something (notice there is no
"to")
Advice And Recommendation :
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11. Should :
+Present , past , future =subject + should +infinitive+…
-Present , past , future = subject + shouldn’t +infinitive+…
? = should + subject +infinitive +…
Ought to :
+Present , past , future =subject + ought to +infinitive+…
+Present , past , future =subject + ought not +infinitive+…
? = ought + subject + to+ infinitive + …
Example : It’s a difficult problem . How ought we to deal with it ?
*after should or ought to we can use a continuous form (be + an –ing form )
It’s half past six already . I should be cooking the tea .
Why are you sitting here doing nothing ? You ought to be working .
Advice And Recommendation :
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12. We use “had better” to say what is the best thing to do in a situation .
Example :
It’s cold . The children had better wear their coats.
My wife is waiting for me . I’d better not be late .
*we could also use should or ought to in these examples although had
better is stronger. The speaker sees the action asnecessary and
expected that it will happen .
+had better + infinitive
-had better not + infinitive
Advice And Recommendation :
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13. Should/ought to have + p.p. verb :
We use these forms when someone didn't do the right thing.
Example :
We didn’t play very well . We should have played better .
I got lost .~ sorry . I ought to have drawn you a map .
It was a lovely old building . They shouldn’t have knocked it
down .
Advice And Recommendation :
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14. Assumption/Deduction
deduction/ dɪˈdʌkʃ ə n / noun [ uncountable
and countable ]
*the process of using the knowledge or
information you have in order to understand
something or form an opinion, or the opinion
that you form : Children will soon make
deductions about the meaning of a word.
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15. Assumption/Deduction
*We use must for logical deduction about the
present , when you want to express certainty :
 It must be very boring to live in a small village
where nothing happens.
*The opposite of must in this case is can’t :
 The letter can’t be from your aunt Harriet . It’s
got a Chinese stamp on it .
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16. Assumption/Deduction
*Use must have + past participle and can’t
have + past participle to make logical
deductions about the past :
 Dave can’t have played football yesterday .
He broke his leg last week .
 He must have escaped through this window.
It is broken.
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17. Assumption/Deduction
assumption/ əˈsʌmpʃ ə n / noun
[ countable ] something that you think is true
although you have no definite proof → assume
assumption that A lot of people make the
assumption that poverty only exists in the Third
World.
My calculations were based on the assumption
that house prices would remain steady.
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18. Assumption/Deduction
*Use may have/ might have / could have +
past participle to make assumptions that you
are not entirely sure about :
 I was expecting a package today , but it
hasn’t arrived . I suppose I may / might
/could have got lost in the post .
- May / might/ could not have + p.p. verb
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