Grammar-Quizzes › Verb Phrases › Verb Groups › Modals › Might have vs. Must have

Might have vs. Must have

Express varying degrees of certainty about past events

What Happened?

MIGHT HAVE
Might expresses an opinion: an uncertain guess, a speculation, based on very little information. Might have expresses an opinion about an earlier (past) situation.
A GUESS
The car driver might have tried to pass between two buses.
One of the bus drivers might have changed lanes without looking first.
The bus drivers might not have been able to see the smaller, lower car.
The road might have narrowed and so they all tried to move into the same lane.

MUST HAVE
Must expresses an opinion: an inference, a conclusion, based on known details. Must have expresses an opinion about an earlier (past) situation.
A CONCLUSION
The car driver must have panicked when he saw the buses moving in on both sides.
The bus passengers must have heard a crunch. (sound)
The car passengers must have escaped out the back. (No other exits were available.)
The insurance company must have declared this car "totaled".

infer (V) – to form an opinion that something is probably true because of information that you have
inference (N) – an opinion that is formed on details or knowledge that you have
panic / panicked (V) – a sudden strong feeling of fear or nervousness that makes you unable to think clearly or behave sensibly
speculate (V) – to guess about the possible causes or effects of something, without knowing all the facts or details
totaled (Adj) – not worth fixing; totally gone

See Modal Review "Degree of Certainty / Possibility"

Must

One word with two meanings

Conclusion vs. Necessity

MUST – CONCLUSION
Must have expresses a conclusion about what happened (past), and is based on putting details and clues together and making an inference (a sure guess).
Traffic officers must be accustomed to seeing occasional bizarre accidents like this one, because they see so many accidents each year
The passengers in the car must have been extremely frightened.

MUST – NECESSITY
Must expresses an opinion about what needs to be done in the present or future, and is based on one's personal sense of what is right and what is wrong.
Drivers must not make unsafe lane changes. (present tense)
Each of the drivers had to file an accident report. (past tense)

Also see Was / Must have / Might have and Should have / Needed to

Sentence Types

Word Order

SENT TYPE	SUBJECT	MODAL	VERB BASE
STATEMENT
guess	She	might	be	upset.
inference	She	must	be	upset.
NEGATIVE
guess	She	might not	be	upset.
inference	She	must not	be	upset.
PAST
guess	She	might have	been	upset.
inference	She	must have	been	upset.
NEG. PAST
guess	She	might not have	been	upset.
inference	She	may not have	been	upset.
W / ADVERB
guess	She	might really have	been	upset.
inference	She	must truly have	been	upset.

Practice

Plane Sight

The title is a play on the words "in plain sight".

plane on highway

What happened?

Select the response from the list that best completes the sentence and fits the situation pictured above.
Compare your response to the feedback by clicking the "Check" or the "Check 1-10" button.

The plane had to make an emergency landing.

Feedback 1

The plane run out of fuel.

Feedback 2

Or the pilot had to land because of an emergency warning .

Feedback 3

Or the pilot confused the highway as the nearby airport runway.

Feedback 4

The drivers on the freeway been surprised to see a plane coming down rapidly in the rear view mirror.

Feedback 5

The plane caused a long traffic jam behind it.

Feedback 6

Afterward, the plane been removed by a truck.

Feedback 7

Or the plane flown away on its own.

Feedback 8

By the evening commute hour, the plane was gone. Drivers been pleased to have the highway open again.

Feedback 9

10.

The story appeared on the evening news. It been a rather memorable day for the pilot.

Feedback 10

Practice 3

Mystery of Hudson Bay Killer Whales

Read the Context

A pod of killer whales was found surfacing through a breathing hole in the ice of Hudson Bay, Quebec. The whales were taking turns rising up through a single hole which was about the size of a pickup truck. The whales (became) trapped by a late winter freeze. Observers thought there (were) as many as a dozen whales including several small ones. Some observers worried that some whales (become) trapped under the ice and died. The mayor of the remote Inuit community called for an icebreaker to save the whales, but none was nearby. Other people made plans to enlarge the 30 by 30 foot ice hole with chainsaws. The mayor was against these plans because they (put) local people in danger of falling into the ice hole. However, changing weather conditions overnight allowed the ice to break up and the whales to escape.

This incident was rare. Normally, as the ice moves in and breathing holes close up, Arctic animals move south. This pod of whales (was) confused. Biologists believed that the late freeze (caught) the whales unexpectedly. With global warming the Arctic area is freezing over later and later.

The area usually freezes over at the end of November. Locals think these whales (stayed) to feed on an abundant supply of seals, sea lions and other small whales.

The local people found that neither they nor the Canadian government was well-equipped to help the whales escape. Had the ice not broken on its own, most of the whales would have died. For the remote Inuit community of Inukjuak, Quebec, this (was) a worrisome experience. Fortunately for all, it turned out well.

"The Mystery of Hudson Bay's Trapped Killer Whales." The Pew Charitable Trusts. N.p., n.d. Web. 02 Jan. 2014. <www.pewenvironment.org>.

Oldenberg, Suzanne. "Stranded Killer Whales Break Free from Hudson Bay Ice." TheGuardian.com. Guardian News and Media, 11 Jan. 2013. Web. 02 Jan. 2014. <guardian.co.uk/environment/2013/jan/10>.

abundant (Adj) – exists in large quantities; more than enough

breathe (V) – take air into the lungs and let it out; respire

chainsaw (N) – small equipment that cuts wood or ice

escape (V) – get away or out of a small space (jail, prison)

freeze (V) – become cold and change from water to ice

icebreaker (N) – a large ship capable of breaking through ice

incident (N) – situation, circumstance; event

Inuit – people of the Arctic; Alaska, Greenland, Canada

locals (N) – local people; people who live nearby

panic / panicked (V) – a sudden strong feeling of fear or nervousness that makes you unable to think clearly or behave sensibly

observer (N) – a person who is watching, paying attention

pod – quantifier for a family of whales or dolphins

remote (Adj) – far away from city centers; distant

surface (V) – rise above water into the air

supply (N) – an amount of something that you are able to use

take turns – one after the other; share in a fair manner

trapped (Adj) – caught within a small space or object

Change the wording to a past modal — might have or must have.

Edit the sentence to include a modal: might have or must have.
Compare your response to the feedback by clicking the "Check" or the "Check 16-23" button.

16.

Local people speculated: the whales became trapped by a late winter freeze.

Edit 16

Feedback 16

17.

Observers guessed: there were as many as a dozen whales including several small ones.

Edit 17

Feedback 17

18.

Some observers worried that some whales became trapped under the ice and died.

Edit 18

Feedback 18

19.

The mayor was against these plans because they (put) local people in danger of falling into the ice hole.

Edit 19

Feedback 19

20.

Biologists inferred: This pod of whales was confused.

Edit 20

Feedback 20

21.

Biologists believed that the late freeze (caught) the whales unexpectedly.

Edit 21

Feedback 21

22.

Locals think these whales stayed to feed on an abundant supply of seals, sea lions and other small whales.

Edit 22

Feedback 22

23.

For the remote Inuit community of Inukjuak, Quebec, this (was) a worrisome experience.

Edit 23

Feedback 23