Common English Words: Permission, Obligation, Prohibition

Permission = It’s OK

English Phrases - Permitted

You can smoke here. (Image source:

English words used for permission:

  • can
  • allowed
  • may
  • permitted

What’s the difference? 

The word “to” is used after allowed and permitted, but not after can or may.

  • You’re allowed to smoke in here.
  • You can to smoke in here.
  • You can smoke in here.

Can is more informal, may and permitted are more formal, and allowed is both formal and informal.

For the past and future of “can,” you can use could / was allowed (in the past) and will be allowed (in the future):

  • When I was a kid, I was allowed to stay up until 11 PM on Friday nights.
  • We‘ll be allowed to check two suitcases on the flight.

Obligation = It’s necessary

English Phrases - Required

You have to show your photo ID.

English words used for obligation:

  • have to
  • need to
  • must
  • required

What’s the difference?

Must and required are more formal than have to and need to.

Don’t use “to” after “must.”

Supposed to / Not supposed to

You can use these words for “light” requirements and prohibitions – for example, rules that are often not followed.

  • We’re supposed to arrive on time, but it’s OK if we’re a little late. Our boss is pretty relaxed.
  • The employees aren’t supposed to eat lunch at their desks, but a lot of them do so anyway.

Prohibition = It’s not OK

English Phrases - Prohibited

You’re not allowed to swim here.

English words used for prohibition:

  • can’t
  • mustn’t
  • not allowed
  • not permitted

What’s the difference?

Can’t is more informal, mustn’t and not permitted are more formal, and not allowed is both formal and informal.

Don’t use “to” after “mustn’t.”


The first “t” in “mustn’t” is silent!

No obligation = It’s not necessary

English Phrases - Optional

You don’t need to wear shoes here.

English words used for no obligation:

  • don’t have to
  • don’t need to
  • not necessary
  • not required
  • optional

What’s the difference?

Don’t have to and don’t need to are more informal. Not necessary, not required, and optional are more formal.

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