Perfect Modals to Express Certainty (Past Possibilities) - English Grammar

Hi everyone. I'm Jennifer from English with  Jennifer. Have you ever experienced something that  

you couldn't explain? I can scare myself quite  well if I let my imagination run away with me.  

That comes from watching too many scary movies.  

When our dog was a puppy, she would sometimes  stop, look up at the stairs, and bark.  

She might have heard something that I didn't hear,  but this happened when I was the only one home,  

so it couldn't have been another  person making noise upstairs.  

What do you think? Could it have been a ghost?

"Might have heard" and "could have  been" are examples of perfect modals.  

Let's talk about using perfect  modals to express past possibilities.

We use perfect modals to talk about the past. We  use a modal verb + "have" + the past participle  

of the main verb. We form the negative by adding  "not." Might not have heard. Could not have been.  

With "could," it's common to use the  contraction "couldn't." Couldn't have been.  

Listen to a few examples. Can you identify  

which verbs express strong certainty and  which ones simply suggest a possibility?

It could have been a ghost.  It might have been a mouse.

It may have been nothing at all.

It must have been my imagination  getting the better of me.

There had to have been a logical explanation.

It couldn't have been another person  because I was the only one home.

What do you think? Well, first let me  point out that I added a semi-modal:  

have to. The past tense is "had to."

Examples 1, 2, and 3 all express less certainty.  

These are past possibilities  -- not strong ones, weak ones.

Could have been. Might have been. May have been.  

I'm just considering ideas. I'm  speculating. This is speculation.

In contrast, "must have been" and "had  to have been" express strong certainty.  

The negative "couldn't have  been" expresses impossibility.

Imagine your friend had a strange dream last night  

about a monkey driving an old  car to get away from a tornado.  

"What do you think it all means?" your friend  asks. Offer suggestions using perfect modals.

Here's my example. You must have felt  worried or stressed when you went to  

sleep. That's why you dreamed about a tornado.  Note how we can also use a progressive form:  

You must have been feeling stressed.  You may have been feeling stressed.  

That's modal verb + "have been" + the  present participle (the -ing form).

Here's one more strange photo.  Tell me why those heads are there.  

Suggest some possibilities and use perfect modals.

Please like the video if you  found it useful and interesting.  

As always, thanks for watching and happy studies!

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