Speculation & deduction
MíriamTomàs
Logical assumptions and
deductions
Expressing speculation or deduction
Depending on the modal verb we use, we’ll express
different degrees of certainty. To express
speculation / deduction, we use: could, may,
might, must and can’t.
There are differences between them; depending on
the one we use we are more sure or less sure about
Almost certain
what we say.
Impossible
actions. Always
negative.
actions.
Can’t
Possible actions.
Must
Could;
may;
might
Logical assumptions and deductions
▪ Must:
▪ is used in affirmative sentences and expresses positive logical
beliefs.
▪ To state something about which you are certain that is true.
must
You have been practising all day,
you must be exhausted!
must
Sean andJennie must be going out again. I’ve seen
them talking very lovey-dovey, you know.
Adding to be + an –ing verb, we
can speculate about an action in
progress
Might and may
I’m calling Jane but I can’t get
through. She might / may be at
class.
We don’t know for sure, but
there’s a possibility.
Can’t and couldn’t
▪ Can’t and couldn’t are used in negations and express negative
logical assumptions.That is to say, you use them when you’re certain
that something is not true or real.
Monsters can’t be real!
Can’t and couldn’t
Someone’s been at home, but it couldn’t beJames, he was at
work.
Should and ought to
Should and ought to are used to describe a situation we expect to
happen.
If I post the letter today, it should / ought to arrive on Friday.
Speculation and deduction in
the past
Do you remember how to form the past
with modal verbs?
These are the modal verbs we need:
▪ Could / couldn’t
▪ Can / can’t
▪ May / might
▪ Must
▪ Should / ought to
You only need to add…
Could / couldn’t
Can / can’t
May / might
Must
Should / ought to
have
Past participle
▪ You can’t / couldn’t have spent very long on this essay –
you’ve only written 100 words.
▪ Lidia must have done something to her hair; she looks
different.
▪ The letter should have arrived by now.
▪ I’m not sure where Jake has gone today. He said he wanted to
go to the movies, but his brother wanted to go for a beer… He
might have gone with his brother at the end.
▪ (We’re not very sure of this because we have mixed
information, but we are guessing).
We could also say: …he may have gone / could have gone…
▪ John and Sarah must have gone back together; I
saw them holding hands this morning.
▪ (We are almost sure about this, because we
have evidence).
▪ My neighbours can’t have gone out! I definitely saw Mrs
Thompson through the window today!
▪ (We are certain that the neighbours were at home, so it is
impossible that they went out)
Adjectives for speculation
▪ He’s bound / sure to be here in a minute. He left an hour ago.
▪ She’s sure / bound to know. She’s an expert on the subject
Be bound + to + infinitive
Be sure + to + infinitive
We are certain that
something is true or will
happen
Adjectives for speculation
▪ I think she’s likely / unlikely to agree to our proposal.
▪ It’s likely / unlikely that the government will raise interests
this year.
Be likely / unlikely+ to +
infinitive
It is likely / unlikely + that +
clause
Adverbs for speculation
▪ She’ll definitely pass the exam.She’s worked really hard.
▪ She definitely won’t pass the exam. She hasn’t done any
work at all.
▪ He’ll probably be here around 8.00. he usually leaves work at
7.30.
▪ He probably won’t be here until about 8.15. he’s stuck in a
traffic jam.