In what situations are both "I" and "me" valid?

Question

I saw this comment by snailplane (emphasis added):

Even when both I and me can be used, I wouldn't call them interchangeable—there's often a difference of register.

When, if ever, is it equally correct to use I or me in a sentence? I cannot think of any examples. I understand there will most likely still be semantic differences between the objective and subjective even if both are grammatically valid; if there are, please explain the semantics as well as the grammar.

My searches on this topic yield only information about the basic differences between I and me, which I already understand.

Answer 1

While both can be grammatically valid in a sentence, I think when using "I" to refer to yourself, you refer to your whole character, your self-image, your identity. Using "me" is closer to "this person here"; it is less ... hm, self-aware, if you will. It distinguishes you from others, but not much more.

As an example, I would like to quote a scene from - yes - Star Trek, where a high-ranking, adorned and much respected embassador makes the official introduction of his wife with the words

May I present she who is my wife, (name).

Of course, this is a little more elaborate than just replacing "me" with "I", but it goes into the same direction.

Edit:
PerryW's "It is I" and "It is me" is a very good example. They both say the same thing, identifying the speaker in response to a question. If that question was, say,

"Who threw that tomato at the speaker?",

they are both valid to identify you as the thrower. However, you would only proclaim "It was I who threw the tomato!" if you are already halfway onto the stage, with a speech of your own explaining your own honest and heartfelt reasons for this offensive act. There is a lot of pathos in saying "It is/was I".

If, however, like most people and tomato-throwers, you just want to make the speaker shut up and leave, a simple "That was me alright!" will do. Or if you immediately regret having thrown it but can't steal away, you may just mumble "me", but not "I".

The situation is the same in the beginning, the message is the same, but using "I" instead of "me" will change how people perceive your answer. In any case, the nominative "I" (or "we"/"she") is very rarely used.

Answer 2

I'll put up an old chestnut, one that is bound to cause argument :)

'It is I' and 'It is me'

Yes, I know about nominatives and linking verbs, but this is clearly a usage that is undergoing change.

As evidence I offer Patricia O'Connor in Woe is I She describes 'It is I' as being almost extinct and says that 'It is me' is now the dominant form.

At the moment, despite the howls of protest from some purists, it seems to be more a question of style than one of 'Thou Shalt'