OBLIGATION & NECESSITY
This modal shows official obligation, often in rules or instructions.
MUST
This modal means a strong prohibition — absolutely not allowed.
MUSTN'T
This modal expresses a recommendation.
SHOULD
This modal is the most common and informal way to give permission.
CAN
This modal shows ability in the present.
CAN
This modal expresses everyday obligation, not necessarily official.
HAVE TO
This modal means something is impossible OR not allowed.
CAN'T
This modal has the same meaning as should, but sounds more formal.
OUGHT TO
This modal gives permission in more formal situations.
MAY
Provide a sentence that uses may or can to give permission
You may use the computer after you finish dinner
This modal means “not necessary.”
DON'T/DOESN'T HAVE TO
This expression means a rule exists, but people often break it.
BE NOT SUPPOSED TO
This phrase warns that a negative consequence will follow.
HAD BETTER
This passive structure means something is officially permitted.
BE ALLOWED TO
Explain the meaning:
“He must live far away.”
The speaker is making a logical conclusion
Rewrite using a modal of obligation:
“It’s required for users to update their data annually.”
“You mustn’t to use your phone here.”
YOU MUSTN'T USE YOUR PHONE HERE.
Improve this advice using the correct modal:
“You maybe want to change your password more often.”
You should change your password more often.
Fix the error:
“You may to join up to five ancestry sites.”
YOU MAY JOIN UP TO
Use must in its “estimate” meaning (not obligation / not deduction).
Correct BOTH mistakes:
“You doesn’t must finish the form before leaving.”
YOU DONT HAVE TO
Identify the difference in meaning:
“You can’t enter.” vs. “You aren’t supposed to enter.”
“can’t” = prohibited; “aren’t supposed to” = rule/expectation that may be broken
Explain the difference:
“You should leave now” vs. “You’d better leave now.”
"should” = advice; “you’d better” = strong warning with implied consequences
You mayn’t bring food into this research area.
You may not
“You can’t to enter unless you may show your badge.”
You can't enter unless you show your badge.