Instructions: Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
Input: Overheard on an elevator today, I didn't realize it was him. Corrected by the know-it-all, He. 'I didn't realize it was he.' The know-it-all then went on a rant about how everybody is a dolt for not knowing that. I swear I have never heard this before in my life. Is the know-it-all correct? If so, why is 'I didn't realize it was he,' grammatically correct? What rule makes 'him' incorrect here?.
Output:
The 'rule' is that the verb to be, in any of its forms, is a copula that takes a predicate rather than an object, hence 'It is I' and other phrases beloved of English teachers in junior schools. There are various theories about the reasons for this, but the truth is that it has become a shibboleth to distinguish those who had 'a proper education' from the hoi polloi who just learned English as they went along. [Another such is to point out that hoi is the definite article in Greek, so 'the hoi polloi' is a tautology; please don't comment to that effect unless you wish to be mocked.] Nobody pretends that this rule is used in everyday speech; Barham's 'Jackdaw of Rheims' has a distinguished audience of prelates and clerics observe a jackdaw His eye so dim, So wasted each limb, That, heedless of grammar, they all cried, 'THAT'S HIM!-- showing that, though you are supposed to know that the 'correct' phrase is 'that is he', you are not expected to use it in moments of stress.