VERY EASY
To talk about future possibility
COULD
To describe past ability
COULD
To express certainty about the past
MUST HAVE BEEN
To express certainty about the present (deductions)
MUST
Describe a past lack of obligation and necessity
DIDN'T HAVE TO
To crticise past behaviour
SHOULD HAVE
To talk about a present necessity, this is also used in suggestions
SHOULD
DIDN'T NEED and NEEDN'T can be synonyms. True or False?
TRUE
To describe possibility in the past
COULD (NOT) HAVE / MIGHT (NOT) HAVE + past participle