the use of may and can as in "can i?" vs "may i?" is another one i see
also who vs whom as in "for whom the bells toll" vs "who is ringing the bells?" is a more complicated one that is beyond me.
and while i am at it, me vs myself is one i have yet to get my head around
...brand new to this forum...I have a pretty good understanding of grammar myself (in a couple of different languages, no less)...forgive my 'misuse' of the ellipsis
; I use it that way to convey an ongoing train of thoughts. Some (belated) answers to these issues:
...These are some good ones. 'Can' and 'may' are often interchanged; technically, that is incorrect. 'Can' implies physical ability; 'may' implies permission. Most often, people use 'Can I?' when asking permission; they should more correctly use 'May I?'.
...'Who' vs 'whom': that is a nominative vs. objective case issue. 'Who' is nominative case; 'whom' is objective. Strictly speaking, 'who' should only be used as the subject of a sentence or clause or as a predicate nominative, and 'whom' as a direct or indirect object or object of a preposition. Both of your examples are grammatically correct:
'Who is ringing the bells?' ('Who' is the subject of the sentence)
'For whom the bell tolls' ('Whom' is the object of the preposition 'for')
Also: 'Who are you?' (predicate nominative; subject is acutally 'you' and 'to be' is an intransitive verb, that is, you cannot use the objective case with it)
'We just found out who the culprit is' (subject of the dependent clause 'who the culprit is')
...'Myself' is a reflexive pronoun rather than the objective pronoun 'me'. It refers an action back to the subject (and is sometimes used for emphasis).
...of course, these lines have been blurred in common speech, and strictly adhering to and insisting on absolutely following rules like this is likely to get you labelled a 'purist' and/or an 'old fogey'...
...also, we must consider the differences between American, British, Canadian, Australian, and other versions of English...they all have slightly different grammatical structures...