"It is I" follows a well-known prescriptivist rule
This question is about prescriptive grammar. It’s a fairly well-known prescriptivist rule that “me, him, her, them” (in other words, pronouns in the objective case) should not be used after forms of the verb “to be” in sentences like “It’s me” or “The culprit is him.” The recommended alternative is to use “I, he, she, they” (pronouns in the nominative case) instead. Constructions of the form “it is me” can apparently be found as far back as the 16th century, but I’m not interested in learning how well (i.e. badly) this rule reflects actual usage. I want to learn more about the prescriptivist rule itself, and what forms educated people have prescribed for various situations. (It’s possible different people proposed slightly different rules.)
For example, I was not aware until recently that the objective case is prescribed after “to be” in sentences of the form “They thought her to be me.” The explanation is that “me” should agree in case with the antecedent “her,” which as the object of the sentence is in the objective case.
This rule is sometimes stated along the lines of "‘to be’ should link two noun phrases of the same case" (from Mark Israel’s "It's me" vs "It is I", adapted from an article by Roger Lustig, referenced in this Stack Exchange question: Which one is correct to say: "It's me" or "It's I"?). However, this is not sufficient as a comprehensive guide to the use of pronouns after to be, because there is not always a nominative or objective antecedent.
I found a grammar book from 1919 that seems to give slightly more guidance: Correct English, Volumes 20-21, edited by Josephine Turck Baker. In general, it follows the principle that “‘to be’ should link two noun phrases of the same case," but it also describes some exceptions.
Here's my summary of its rules, based on the examples given (I think the book's wording of the rules is unhelpful, as some of them falsely appear to contradict one another):
My interpretation of the rules in "Correct English"
Pronouns should be in the nominative case after
- am, is, was, were
- have been, has been, had been
- can be, could be
- may be, might be
- shall be, will be
Example: “I hardly think that it was he to whom Mr. Blank referred.” I would assume the author left out some combinations of modal verb and "be" from this list merely for reasons of space, so it should be read as including should be, would be, etc.
Pronouns should be in the objective case after “to be” when it is immediately preceded by an antecedent in the objective case.
Example: “They supposed it to be me.”
Pronouns should be in the nominative case after “to be” when it is not immediately preceded by an antecedent in the objective case, and it is preceded earlier in the sentence by an antecedent in the nominative case.
- "It was thought to be he to whom the speaker referred."
- "I should like to be he."
- "Do you think that you should like to be he?"
It seems possible that sentences such as “I am free to be I” (which seems to be the same in structure as the first sentence, aside from substituting an adjective for a participle) would also fall under this category, although unfortunately no examples of this type are given. (if so, it would contradict this Grammarphobia post.)
Pronouns should be in the nominative case after “being” when it is immediately preceded by an antecedent in the genitive case.
Example: “I had no thought of its being he.”
These rules still leave a gray area, however.
What form "should" be used where there is no antecedent of any kind?
In particular, I've thought of two cases:
What form did people prescribe after “being” when it is not preceded by an antecedent of any sort?
Being [he/him] is not easy.
What form did people prescribe after “to be” when it is not preceded by an antecedent of any sort?
To be [he/him] is not easy. It is not easy to be [he/him].
“It” is not an antecedent in the second sentence, as we can see from sentences such as “It is not easy to like her.”)
There is precedent for the use of the nominative after the copula without a nominative antecedent in sentences like “I had no thought of its being he.” I’m not sure why the nominative is prescribed here—it clearly would be ridiculous to use a genitive pronoun after the copula in such circumstances, but why not an objective pronoun?—but in any case, that’s clearly established in the book. So it seems a minor extension to use the nominative in sentences “Being he is not easy.” And in fact, the way the rule is phrased in Correct English suggests this: "A noun or pronoun after the verb be in the gerundial construction (being) is in the nominative case." It still sounds odd though, and there are no example sentences like this in Correct English (all of the example sentences have genitive pronouns before the gerund), so I’d like to know if it was actually prescribed by other sources.
The construction with “to be” is different. My best guess is that we would suppose an elided subject such as “[for me] to be” which would suggest the use of the objective case (“It is not easy [for him] to be him.”). But that assumption seems like it could also apply in sentences of the type *“I should like [for me] to be him,” and yet Correct English nonetheless prescribes the nominative case for the predicate noun in this sentence.
The situation in Correct English is confusing because at one point, it says "as the objective case always precedes the infinitive verb, the objective case must always follow the infinitive verb," and later on it says "The pronouns I, he, she, we, they follow to be when to be is not preceded by a noun or a pronoun." This is the apparent contradiction I was talking about earlier; you should look at it in context to see if I'm misinterpreting it. All of the example sentences where a nominative pronoun follows to be actually have nominative nouns or pronouns earlier in the sentence that can serve as antecedents, so it's not clear to me if this rule is meant to be exceptionless, or confined to certain grammatical contexts.
The kind of answer I'm interested in
As I said up top, I don't want to hear about actual usage or practical advice. I'm interested in learning what people have said is "correct" in these circumstances (preferably with examples, to make the construction totally clear). The more well-known or influential the prescriptivist, the better.