Can or May?

by Craig Shrives

What Is the Difference between "Can" and "May"?

"Can" and "may" are both used to ask for permission, but this has not always been the case. In the past, there was a clear distinction between "can" and "may." "Can" was used for ability (e.g., Can you swim?), and "may" was used for permission (e.g., May I swim in your lake?).

As this distinction is still observed by some, the following guidance is appropriate:

May for Permission

In a polite or formal setting, use "may" for permission. For example:
  • May she swim in your pool?
  • (This means "Is she permitted to swim in your pool?" It sounds polite.)

Can for Permission

In an informal setting, it is safe to use "can" for permission. For example:
  • Can she swim in your pool?
  • (This means the same as the one above. It sounds neutral as opposed to polite.)

Can for Ability

Use "can" for ability. For example:
  • Can she swim?
  • (Is she able to swim?)
  • Can she do quadratic equations?
  • (Is she able to do quadratic equations?)
You cannot use "may" to express ability.

More about "Can"

The word "can" is a modal auxiliary verb used to express ability. For example:
  • I can whistle. correct tick
  • (I have the ability to whistle.)
  • Can he lift 150 kgs? correct tick
  • (Does he have the ability to lift 150 kgs?)
"Can" can also be used to express permission. For example:
  • You can stroke the ponies but not goats. correct tick
  • (Here, "can" expresses permission. "Can" tends to be used for permission among friends or in an informal setting.)

More about "May"

The word "may" is a modal auxiliary verb used to denote permission. For example:
  • You can swim in this river. correct tick
  • (You are allowed to swim in this river.)
  • May I have a biscuit? correct tick
  • (Am I permitted to have a biscuit?)
If you have a reason to be "├╝ber correct" (e.g., you're hosting royalty or a very pedantic grandparent), you should use "may" and not "can" to express permission. It is true to say that "may" and "can" are interchangeable to express permission nowadays.

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