Transcript Can`t have
ABILITY
CAN and BE ABLE TO- present
We use can or be able to say that someone
has an ability
Ex. James can/is able to play chess but he
can’t/ isn’t able to ride a bike
ABILITY
CAN and BE ABLE TO – past
We use could or was able to to say that
someone had an ability in the past
Ex. He could/was able to read when he
was three but he couldn’t/wasn’t able to
catch a ball when he started school
ABILITY
We don’t use could to talk about one
occasion in the past but we can use
couldn’t.
Ex. She was able to (not could) come to the
meeting but she couldn’t stay for lunch
ABILITY
BE ABLE TO – other tenses
Can is only used in the present tense and
could is only used in the past. In all other
tenses you use be able to.
ABILITY
• I will be able to give you a lift on my way
to college. (future)
• They haven’t been able to contact Mary
because of the storms. (present perfect)
• If you saved enough money, you would be
able to visit me in New York. (conditional)
• They hope to be able to visit me next
year. (infinitive)
OBLIGATION
For obligation, we can often use must and have to:
I must go now or I’ll miss the bus.
or I have to go now or I’ll miss the bus.
We use must to give orders or strong advice, including to
ourselves
You must tell me everything. (= I feel strongly about
this)
She must be home by midnight. (These are my
instructions)
You must come to the hotel one day. (= I strongly
advise you to)
I must go now. (I have decided to do this)
OBLIGATION
When there is a rule or where the obligation
does not come from the speaker have to is
more usual:
You have to pay to park your car here. (= this
is a rule)
I have to stay until the food is cooked. (= this is
part of my job)
We usually use have to for habits:
I have to get up early to cook breakfast.
OBLIGATION
We only use must in the present tense.
In all other tenses, we use have to:
I had to work every day. (past simple)
I’ll have to work longer hours. (future)
I avoided having to speak to him by
crossing the street. (verb+ -ing)
If I got the job, I’d have to buy a car.
(conditional)
OBLIGATION
MUSTN’T and DON’T HAVE TO
Mustn’t means “ don’t do it”
Don’t have to means “it’s not necessary to
do it”
I mustn't wear jeans at work. (= it is
wrong to do this; it isn’t allowed)
You don’t have to stay at school until you
are 18. (= you are not obliged to but you
can if you want)
DEDUCTION:
CERTAINTY
Talking about the present
We use:
must when we know something is
true
can’t/couldn’t when we are sure
something is not true.
DEDUCTION:
CERTAINTY
This man is looking at a letter with an Australian
stamp which has just arrived for his son.
It must be from his
girlfriend because
she’s in Australia.
(I am certain it is from
her)
It can’t be /couldn't
be from his girlfriend
because that’s not her
handwriting.
(I am certain it’s not
from her)
DEDUCTION:
POSSIBILITY
Talking about the present
We use:
might/may/could when we think
something is possibly true
might not/ may not when we think
something is possibly not true
DEDUCTION:
POSSIBILITY
The letter
might/may/could be
from his friend Tony,
because he moved to
Australia recently.
(= I know that Tony
lives there and it is
possible not certain,
that the letter is from
him)
It might not/may
not be from anyone
that we know.
(= It is possible that
it is not)
DEDUCTION:
CERTAINTY &POSSIBILITY
PRESENT
TRUE
NOT TRUE
CERTAINTY
Must +infinitive
without to
Can’t/couldn’t
+infinitive without
to
Might/may/could
+infinitive without
to
Might not/may
not
+infinitive without
to
POSSIBILITY
DEDUCTION:
POSSIBILITY
Notice that could means the same as
might and may, but couldn’t is different
from might not and may not.
DEDUCTION
CERTAINTY &POSSIBILITY
All the verbs in the box above can also
be followed by be +verb+ -ing:
His girlfriend might be travelling home
at this moment
DEDUCTION
Talking about the future
We also use might(not), may(not) and
could when we are not certain about
the future:
James might go to see his girlfriend in
Australia next month.
Steve is making a journey across
Australia by car from Sidney to Perth
DEDUCTION:
CERTAINTY
Talking about the past
We use:
must have when we are sure something is true:
Steve must have arrived in Perth by now. (= I’m
certain he has arrived)
can’t have/couldn’t have when we are sure
something is not true:
He can’t/couldn’t have got there yet because it
will take at least two weeks (=I’m certain he
hasn’t got there)
DEDUCTION:
POSSIBILITY
Talking about the past
We use:
might have/may have/could have when we
think something is possibly true:
He might/may/could have stopped for a few
days on the way. (=it is possible)
might not have/may not have when we think
something is possibly not true:
He might/may not have had time to do
everything he wanted. (=it is possible he didn’t)
DEDUCTION:
CERTAINTY &POSSIBILITY
PAST
TRUE
NOT TRUE
CERTAINTY
Must have
+past participle
Can’t have/
couldn’t have
+past participle
POSSIBILITY
Might have/
may have/
could have
+past participle
Might not have/
may not have
+past participle
DEDUCTION:
POSSIBILITY
Notice that could have means the same
as might have and may have,
but couldn’t have is different from might
not have and may not have.