For those who seek direction but don't wish to read more than necessary, I will offer a brief prescriptive advice on what to say or write, but do not mistake this advice as implying that other forms are incorrect or that other usage is inferior in all circumstances.
Terms for cases for this writ:
rectus = subjective = nominative
oblique = objective [term used inconsistently] = nonnominative cases
When you encounter the verb 'to be' where it is preceded by a subject and followed by a personal pronoun and the pronoun is not followed by another verb, use the oblique case for the pronoun if it is not possessive.
For the format
[Subject] [to be] [Pronoun].
Examples of proper and correct usage are:
It is me.
This is him.
That is her
________________
Now for the fuller story on usage and correctness.
For a large portion of speakers, use of the subjective case implies a formal style/register/tone if it is recognized as correct at all. Its use is scarce presently. It is sometimes perceived as archaic.
Grammarians created prescriptive rules that prescribed the subjective case be generally used.
Considering popular use, at the time the grammarians created this rule it was unjustifiable as a rule regarding correctness. It could not be justified to consider noncompliant sentences as incorrect and it still can not be. The incongruity between these rules and the reality of english usage has created disputes for hundreds of years.
As Joseph Priestley published in 1772 in
You can get free software to view DjVu documents such as the preceding one.Joseph Priestly wrote: The Rudiments of English Grammar,
Third Edition
Ⅲ. Of the Oblique Cases of Pronouns
Page 104:
All our grammarians say, that the nominative cases of pronouns ought to follow the verb substantive as well as precede it; yet many familiar forms of speech, and the example of some of our best writers, would lead us to make a contrary rule; or, at least, would leave us at liberty to adopt which we liked best.
The rule to use the subjective case is an example of
-- Sci.Lang FAQSci.Lang FAQ wrote: Pure inventions of self-appointed grammarians with no basis in actual usage:
3. "It is I"
A good resource especially for foreigners for learning about English personal pronouns is done by
Warsaw Will
Because of rule dictating subjective case, some people have the mistaken belief that other usage is incorrect. Furthering this perception is a tendency to confuse style formality with correctness.Warsaw Will wrote:In few areas can the divide between traditional grammar and actual usage be as wide as in the 'case' of personal pronouns. … But not surprisingly most of us nowadays treat 'be' like any other verb in this respect and are using object forms, just as in the examples above.
The following statement is untrue.
I know academia and especially schools of Science well enough that I know this to be untrue. The rule prescribing subjective case is not always followed and I expect that it most often not.Mad Harlequin wrote: In academia and other formal circles, you will not see anyone saying "It's him!"
There may be variation by a combination of region and maybe gender.
There is a report from someone claiming much experience telephoning to Britain and the USA that speakers of British English would never answer a caller with "This is he." or "This is she." He heard "This is she." from some American women.
Following, I present some excerpts from and links into the same discussion. I do not endorse everything which I copy here. I will start with the highest voted post in the entire discussion. My own writing ends here.
________________
mofei
The last comment from goofy is absolutely right. If "This is she" is grammatical (as the Chicago Manual of Style says) then it isn't consistent with general usage of the verb "be". I suppose you could call it an idiom, or more likely, snobbery.
English is a Germanic language, and in general Germanic languages take the nominative case for the object (sometimes called predicate) of the verb "be". Modern German does for all objects of "be", not just pronouns.
Old English did this too, but in the middle ages, English started to change under the influence of French and started using the accusative (me, her, him, us, them) after "be" instead of the nominative (I, she, he, we, they).
If it was true that modern English took the nominative after "be", we would say things like "That's they over there" or "The man who murdered Poirot is he!".
So if anyone tries to tell you that "This is she" is really their natural way of speaking … they
a) have been dead for several hundred years
b) are a snob
c) have had this rule shoved down their throat by a snob
________________
John Anderson
Everyone around me says "this is her." No one says "this is she." If the traditional rule differs from what people say, that tells me that something is wrong with the rule, not the speakers.
________________
John
The rule ignores the facts of usage. The fact is that native speakers do not say:
That's I.
The best swimmer is he.
The winners are we.
Some speakers of course do say these, but I'm claiming that if they do, they say them because they've been explicitly taught that these forms are "correct."
________________
John Anderson citing
Merriam-Webster's Dictionary of English Usage page 568:
Clearly, both the it is I and It's me patterns are in reputable use and have been for a considerable time. It is I tends to be used in more formal or more stuffy situations; it's me predominates in real and fictional speech and in a more relaxed writing style. Him, her, us, and them my be less common after the verb to be than me is, but they are far from rare and are equally good.
________________
JJMBallantyne
"The verb 'to be' does not take an object."
Then "him" in the following example should be "he"?
I would not want to be him.
________________
UIP
-Pretty much everyone says "her".
-"She" sounds funny.
-"To be" takes the objective case in other situations, such as "That's him over there"
-The object of a verb takes the objective case, and this gives every indication of being the object, so it takes the objective case.
In favor of "she"
-Because I said so.
…
So, "to be" is special type of verb, that follows rules completely different from the rule that all the other verbs follow. Why? Because I said so. The idea that because they are interchangeable in FACT, they must be the same GRAMMATICALLY is absurd. According to that logic, every noun should take exactly the same pronoun regardless of its case. And if they are truly interchangeable, why must they take the same CASE, but not the same PERSON?
________________
goofy
I agree that "I" is nominative and "me" is accusative. What I don't agree with is that the nominative must follow the verb "be". What is the evidence for this? Accusative pronouns have been used after "be" since the 1600s. Dictionaries and usage books recognize it as correct, at least in some contexts. My understanding is that the "rule" that "be" must be followed by the nominative is based on an analogy with Latin.