Learn English – Is ‘can’ an appropriate substitute for ‘may’ to indicate possibility?

synonymsword-choice

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?

Best Answer

They are not exactly the same. The wording in the dictionary entries are also somewhat different so they point to different aspects of the similarity and differences.

sometimes used interchangeably with may

Means that in some cases they can be used for describing the same thing, but this depends on context, and possibly some re-phrasing needed to keep same meaning.

Not to be used as a substitute for may.

Means that is not exactly the same, so you can not just switch the words in any context.