“Predicate nominative” is the term you want to search for. Most people do not talk this way, and I think the objective case will eventually be fully accepted even by the more stubborn of the prescriptivists. But the idea is that what follows the linking verb is not an object, but rather the complement/equivalent of the subject, so it should remain in the subjective/nominative case. It certainly makes logical sense, but language need not be logical.
What’s so confusing? What you call “traditional”, I call “outdated”. You don’t see anyone running around saying “methinks”, do you? No, because usage dies. Unless you introduce yourself on the phone with “Hey, it’s I”, you can’t honestly think that this rule exists anymore.
OP, the rule is if your age is triple digits, you use “It was I,” but if you were born after WWI, it’s “It was me.” You can try to get by with archaic rules of predicate nominatives, but frankly, I think we should just let that one die.
Ha ha ha.
This reminds me of Robert Siegel saying “Attorney Generals” on the radio, followed by hordes of angry nerds informing him that the correct pluralization is “Attorneys General.” Whatever, angry dorks, go write your Congressperson or something. Nobody speaks that way. Not that I’m comparing anyone here to the gang of copy-editing dweebs who could not fight their compulsion to write letters and make phone calls to NPR about the world’s silliest grammatical error; the story reminded me of this, is all, as this strikes me as another technical rule of language that no normal people actually employ. I always say “It’s me” and would say “The member is me,” rules be damned.
I wouldn’t use I or me. I’d simply list my own name among the attendees.
My apologies to those who answered the pre-edited version (so quickly that the edit window was still active). I was providing the answer to a colleague who gave me one version, then the second with the committee members in the sentence.
Thank you to all.
That’s kind of funny. I remember listening to the first broadcast–it was just a few weeks ago, IIRC. His use of “attorney generals” actually stuck out for me. It’s the pluralization I prefer, but I was kind of surprised to hear NPR using it. I figure if anyone uses “attorneys general,” it’s going to be NPR and The New Yorker. (And, to be fair, I seem to recall Robert Siegal saying “attorneys general” the first time he used that phrase, but then “attorney generals” in all subsequent references.)
Sure enough, on the next program, I hear about those angry hordes of grammar pedants writing in. I’m glad that NPR stuck to their guns and said both forms were acceptable.
Spoken and written are two different things. I might speak incorrect much of the time, but I always make an effort to write correctly-- especially in a professional context, which is, apparently, what the OP is asking about.
Finding the right spot on the scale from archaic-obsolete-old-fashioned-formal-informal-casual-colloquial isn’t always easy. This isn’t a digital switch that has only 0 and 1 as positions.
Reginald Hunter is a black American comedian who has lived much of his life in England and he often includes differences in speech patterns in his standup. He has a bit in which he talks about an English person asking what he knew about someone (I can’t remember who it was).
Hunter: “I know he dead.”
English person: "I know this is terribly English of me, but I just have to say that correct grammar would be ‘He died.’ "
Hunter: “Well, at first he died. Now he dead.”
This is a good illustration of differing grammar in different registers of speech.
For those saying that “It is I” is dead and buried and should unequivocally be replaced by “It is me” in all situations, I ask, what about “he dead”? That’s a perfectly good colloquial use in one English dialect, which allows for such constructions and even incorporates nuances of grammar that are more subtle than in standard American and British English. (In black American vernacular, for instance, he dead, he be dead, he be dying, etc., can carry slightly different connotations.)
On the contrary, the “rule” is “It was I.” You can argue the rule is archaic, that predicate nominatives should go off and die, etc., but the “rule” is still out there. Frotunately, the grammar nazis don’t have arrest powers, so you’re free to write a sentence any way you want. Just don’t declare the rules to be dead simply because you don’t like them.
Are you being serious?
Edit: @ Ascenray
The real rules of grammar are the ones that people actually follow. If it’s something that people used to follow, then it’s something that was a rule of grammar, but isn’t any more.
The predicate nominative is a bit of a tricky one, in that both usages are still not uncommon. I would advise to use the old rule in a more formal situation, or the new rule in a less formal one. Or, if you work for a newspaper or the like, to go with what their style guide says.
The spelling police, however, are a horse of another colour. You may make one phone call. 
Well, you do hear the occasional “methinks.” 
Usage dies, but this particular usage hasn’t given up the ghost yet. There is also a difference between usage in casual conversation and usage in formal writing. As I said, I will say “it’s me,” but the OP is writing a letter. I think it makes sense to err on the side of caution and stick with what is considered proper formal usage.
On preview (I got interrupted), I see this has been covered, but this is my take on it.
Of course I’m being serious.
You’re seriously asking if something as wildly grammatically wrong as “he dead” should be accepted as “he is dead” because there are certain people who use this construction conversationally? “He dead” is not nearly as universal in its use as “It is me.” Tiny fringe groups and isolated usage are not what cause shifts in acceptable language.
Exam: Read the above passage and answer the following questions fully and offering evidence-based support and arguments.
(a) What are the linguistic boundaries of the following terms as they are used in the passage,
(b) how are such boundaries scientifically arrived at, and
© how are such boundaries supported by data? –
– “Wildly grammatically wrong”
– “nearly as universal”
– “tiny fringe groups”
– “isolated usage”
Before I even bother with this silliness, are you going to tell me that “he dead” as a substitute for “he is dead” is as commonly used as “it is me” in place of “it is I”?
Just because it’s not standard English doesn’t mean that something isn’t “acceptable.” In much of the AA community, “he dead” *is *acceptable. And AA dialect does have grammar and rules-- and even if those rules aren’t in line with Standard English, they do exist. In certain communities, “He dead” *is *as accepted as “It is me.” Just because you don’t belong to such a community doesn’t make it a fringe group or “isolated.”
No it’s not. Some people may use that very colloquially, but generally people do not accept that as proper, not even what you call the “AA community” to which I belong, for the record.
My style guide says re-write the sentence so I can figure out which one to use. 