Modals in the Past

Grammar Reference

	Form	Example
would have + pp	Unreal/imagined past result	I needn't have bought a ticket — it was free.
should have + pp	Past regret / complaint	I didn't need to buy a ticket — my brother had one.
shouldn't have + pp	Regret about past action	I would have gone.
needn't have + pp	Did it — but unnecessary	You should have told me.
didn't need to + inf	Didn't do it — not necessary	I shouldn't have eaten it.

Tap the best option based on the context.

Carbon emissions rose 12% last year. The government ______ seen this coming — the data was clear.
(should have / must have / might have)
The company's data was exposed. They ______ invested in cybersecurity — it was clearly a risk.
(should have / can't have / might have)
She turned down three job offers. She ______ been very confident in her skills to do that.
(must have / should have / can't have)
The algorithm they used ______ been tested properly — it crashed immediately on launch.
(can't have / must have / should have)
The fall in biodiversity ______ been caused by deforestation — there are several possible factors.
(might have / must have / should have)
The workforce ______ been better prepared for automation — the warning signs were there for years.
(could have / must have / can't have)
She achieved carbon neutrality for her start-up in under two years. It ______ taken enormous effort.
(must have / can't have / might have)
The inequality data ______ been more widely shared — it was available to all researchers.
(could have / can't have / must have)

Use must have, should have, could have, might have or can't have.

The government ______ acted on fossil fuels decades earlier — the science was clear.
That data breach ______ been an accident — it was far too deliberate.
The entrepreneur ______ worked around the clock — she delivered in half the time.
The fall in carbon emissions ______ been caused by the new renewable energy policy, but we need more evidence.
Companies ______ introduced retraining earlier — many redundancies were predictable.

I'm sure the algorithm was not tested properly before launch. HAVEThe algorithm ______ properly before launch.
It was a mistake not to tackle inequality earlier. SHOULDWe ______ inequality earlier.
Perhaps the deforestation was caused by illegal logging. MIGHTThe deforestation ______ illegal logging.
It's impossible that she knew about the data breach before it was reported. HAVEShe ______ about the breach before it was reported.