Modals for permission and ability (can, could, may)

Modals are very common in the English language, specifically when we use them to ask for permission in the present or future tense. Use them like auxiliary verbs, before a base form of the verb. Use table 17 to complete the exercises in this module.

Subject (I) + modal (will) + base verb (go)…

Modals in red are formal

Modals in blue are informal or neutral

Modals Uses Affirmative form examplesNegative form examplesQuestion form examples
Be allowed to 
Used in the same way as can or can’t(talking about rules).You are allowed to smoke here.You aren’t allowed to smoke here.Are we allowed to smoke here?
Can / Can’t Giving permission,enforcing rules.You can turn on your cellphone now.You can’t park here.Can we park here?(is it allowed?)
Could Making suggestions, asking for permission
I could try to call him at home.Cannot be used in the negative form when talking about permissionCould I have some water, please?

Giving/asking for permission, talking about rulesYou may use the pool until 9:00PM.You may not sit here.May I speak with Mr. Mitchell, please?
Might Making predictions that are uncertain(50%). Asking questions (rarely)about possibilities.I might need your help with something.
I might not finish on time.Might I help you with that?

Used to talk about rules. Asking about obligation (very rare)You must be home by 11:00PM.
You mustn’t leavefood on your plate.Must I finish this report before leaving?
Be To Talking about rules. Very strict, more formal than must. Asking for orders (very rare).You are to wash your hands every time you use the bathroom.You aren’t to disturb your neighbor at night.Am I to stop what I am doing and follow you?
ShouldGiving/asking for advice or talking about rules. Less strict than must.You should wear a sweater when it’s cold.
You shouldn’t take so many pills because it’s bad for your health.Should I use a black pen to sign the contract?
ModalsCan / Can’tCould / Couldn’tMay / May not
UsesAsking for permission, giving permission, expressing ability (positive and negative) Asking for permission, expressing ability (past)Asking for permission, giving permission.
FormalityInformalFormal when used for permissionVery formal
Asking for permission:Can I have a pencil, please?
Giving permission: Yes, you can have a pencil. 
Expressing ability (positive):I can type very fast. 
Expressing ability (negative):
I can’t speak Spanish. 
Asking for permission:
Could I borrow your laptop for a minute?
Expressing ability (past):
You could see better when you were young. 
I could speak five languages when I was a child. 
Asking for permission:
May I ask you some questions?
Giving permission:
You may talk to my lawyers. 
NOTE- It’s impossible to use ‘may’ in the past.