Strictly speaking, can is an auxiliary verb that is used to express mental and physical capability. May is an auxiliary verb that is used to express permission. However, the sharp dividing line between the use of can and may has eroded, due to the English language’s seeming evolution toward informality.





Today, can is used to express mental and physical capability and in informal circumstances, it expresses permission. A child might ask a teacher, “May I have an apple?” as the child is asking a superior if he will be allowed to receive an apple. A child might ask another child, “Can I have an apple?” as he is speaking to a peer.






May is more polite than can, it is used in situations of courtesy, formality and making requests of superiors in age or rank.