UNIT 6: MODALS TO EXPRESS DEGREES OF CERTAINTY

• For me is important to know that we have to use

MUST HAVE /HAD TO HAVE” + PAST PARTICIPLE

When we are speculating about the past and are almost certain.

For instance:

A: I am sure that I turned on my TV.

B: Do not worry. Your husband is here and he must have turned it off.

• Also let me tell you that when we speculate in negative about the past we have two possibilities:

COULDN’T HAVE

CAN’T HAVE

Both have the same meaning.

For instance:

Oh! It is a disaster but my brother was outside yesterday, so he couldn’t have done it.

Or

Oh! It is a disaster but my brother was outside yesterday, so he can’t have done it.

• When you are slightly less certain, you have to use

MUST NOT HAVE + PAST PARTICIPLE

For instance:

My uncle must not have traveled to Loreto.

• In questions we use
  
  CAN HAVE/ COULD HAVE + PAST PARTICIPLE
  
  For instance:
  Could / Can that have discovered the penicillin?
  
  Vanessa Correa - AO4