One definition of can in Merriam-Webster Online is:
c —used to indicate possibility < do you think he can still be alive> < those things can happen> ; sometimes used interchangeably with may
But in The Elements of Style written by William Strunk, Jr., it says:
Can. Means am (is, are) able. Not to be used as a substitute for may.
This contradiction makes me confused. So in what situation can can be used "interchangeably" with may, and in what situation it cannot?
EDIT: The two sentences in The Elements of Style make me feel that the author permits only one use of can (be able) in the first sentence and proscribes the other use (may; to indicate possibility) in the second sentence. Did I misinterpret the author's meaning? Or the text is ambiguous?