''In English, the nominative case is the case of a pronoun used as the subject of a finite verb (as in; I wrote the letter) or as a predicate nominative (as we in: It is we who have made the mistake). The nominative case stands in contrast to the objective case.'' (American Heritage Guide to Contemporary usage and Style)
Is this true?
Does anyone say'' It is we who have made the mistake'' these days?
>>Does anyone say'' It is we who have made the mistake'' these days?<<
Only in markedly formal and almost archaic speech; even your usual formal speech normally does not have such in practice (at least in North American English) but rather has shifted to using the oblique case for the objects of predicative verbs.
(Note that I say "oblique" rather than "objective" because it is used for far more than just direct and indirect objects, and can even be used for subjects in clauses with multiple subjects in coordinate constructions.)
<<Does anyone say'' It is we who have made the mistake'' these days?>>
As Travis said, that's a very formal way of putting it. You're more likely to hear "It was us who made the mistake" or simply "We made the mistake".
"It was we..." sounds very unusual to me, even though it's the same sentence pattern as "It was I..." I would reword the sentence: "We were the ones who...", or, as Josh suggested, simply, "We made the mistake".
It's normal to say: It is he/she when someone calls you and wants to talk to you (''I would like to talk to John/Sally''.... - This is he/she). Educated people do it all the time.
Yes, but that fact doesn't make "It is we who have made the mistake" sound any less weird. Same grammatical construction, but different pronoun and different context.
>>It's normal to say: It is he/she when someone calls you and wants to talk to you (''I would like to talk to John/Sally''.... - This is he/she). Educated people do it all the time.<<
For starters. just what do you mean by "educated", anyways? At least around here, saying things like "This is he" is only a rather stilted and archaic formalism and does not make one any more "educated". Even in most formal speech one does not normally say such here, no matter how educated the speaker is; hell, you hear "shall" used far more frequently here, and "shall" has been largely replaced by "will" and "be going to" in most speech outside of rather poetic or emphatic usages. Of course, there is the minority which does use such, but honestly it sounds silly, in such being more just a matter of the intransigence of a few against the acceptance of the use of the oblique case with objects of copulative verbs (which has long since occurred for the general population).
>>Yes, but that fact doesn't make "It is we who have made the mistake" sound any less weird. Same grammatical construction, but different pronoun and different context.<<
The underlying principle is the same, which is whether one is to use nominative case or oblique case with the objects of copulative verbs. In normal usage, even in formal speech, the oblique case has long since replaced the nominative case for the objects of copulative verbs. However, there are the self-proclaimed "educated" who have declared that using nominative case in such cases is the only "correct" way to form clauses where pronouns are used as objects of copulative verbs. Of course, such "educated" individuals are only in denial about actual English usage, and are effectively trying (futilely) to turn back the clock centuries, considering that the oblique case has already been found in such positions, in alternation with the nominative case, for centuries.
Right, but "It was I..." still sounds much more natural than "It was we...", probably because we hear phrases like "It is I" but we seldom hear "It is we".
I do agree that we should simply re-analyze "be" as an ordinary transitive verb instead of a special copula thingie and be done with it, by the way. Even the English teachers who seem to think otherwise make this "error" all the time without realizing it. Ask one to point out somebody in a photograph, and they will say "That's him", never "That is he".
By the way, I remember watching the Price is Right years ago -- it was a long time ago, perhaps ten years or more -- and Bob Barker made an odd hypercorrection: "You did this because of I?" It sounded so strange to my ears that I still remember it.