One can use 'except' as a preposition, as in the following sentence:
I gave everyone except Mary a present.
Changing 'Mary' for a pronoun we get:
I gave everyone except her a present.
Clearly the following is wrong:
*I gave everyone except
So my question is: does except always take the objective case in English? Consider the following sentence:
All except him agreed
To me, "he" sounds more elegant here, so maybe the noun affected by 'except' keeps the same case it would otherwise have in the sentence. But then:
Except I, we all agreed
sounds definitely wrong compared to "Except me, we all agreed." Perhaps it is not a matter of case at all, but something else? I found this question very hard to google for, so that's all I've got to bring to the table.