[peteryoung]

I read this theory about difference of 'CAN' and 'MAY', but I don't quite understand it. Could you please help me? I really appreciate it.

The excerpt from the book:

A further difference between dynamic/deontic CAN and deontic/dynamic MAY is that the former may be what Palmer calls 'subject-oriented' - i.e. it may 'relate semantically to some kind of activity, quality, status, etc. of the subject of the sentence', whereas MAY is never subject oriented. In the present account, this phenomenon may be represented as a contraint on the possible values of the C variable such that in the case of CAN, C may represent either some circumstance which originates within, but need not be under the concious control of, the referent of the subject of the sentence, as in:
a)He can speak fourteen languages
b)What can you contribute to the discussion?
or else some circumstance which originates outside the referent of the subject, as in:
c) You can go now, thank you.
d) She can be the bus driver and I can be the ambulance driver.

With MAY, on the other hand, the state of affairs represented by C is always external to the referent of the subject
e) He may speak fourteen languages
f) What may you contribute to the discussion?



What puzzles me most is the difference between a)b) and e)f). I used to think 'may' here is a formal/polite version of 'can' and that's all. But it seems there is this orientation problem. What does the author mean by saying a) and b) are subject-oriented? Would appreciate any reply. Thank you.