Your intuitions about the grammaticality of your four examples aren't quite right. Sentence (4) is ungrammatical. The reason is that the verb SAY needs a Complement (under some grammatical analyses we'd say it needs an Object). The phrase that the world will end is a Complement in example (3), but with confidence in number (4) is an Adjunct. It's not a grammatically essential part of the sentence. So example (3) is grammatical and (4) isn't.
Unfortunately, the phrase heavy noun phrase shift was coined before the more modern interpretation of noun phrase used by linguists such as Huddleston & Pullum (2002, 2005). For these more recent writers noun phrase refers to a phrase headed by a noun. For earlier scholars a noun phrase didn't necessarily involve anything like a noun at all. A noun phrase was just a phrase with the grammatical function of Subject, Object or "Object" of a preposition. It could quite easily be a non-finite clause:
- Her leaving so early annoyed me.
The term heavy NP shift, therefore, also includes the postposing of clauses functioning as internal Complements of the verb. Sentence (2) therefore could indeed be said to be an exemplar of heavy NP shift, even though many modern grammarians would not actually regard that the world will end as a noun phrase. It isn't a phrase headed by a noun.
In short what allows us to move the clause functioning as Complement of the verb is indeed the fact that it is heavy, in other words long (it is several words long). Compare the following examples with (1, 2):
- I can say that with confidence.
- *I can say with confidence that. (seems ungrammatical)
Here where the Complement of the verb SAY is short, we don't seem to be able to move it to the end of the sentence.
None of these uses are clear, idiomatic English.
What is the correct tag question of proverbs like (a) None is none under the sun,isn't it/ are they? (b) Time and tide wait for none, isn't it/ do they? (c) Waste not, want not, isn't it?
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I've given the answer with confusion. I think that as the proverbs are universal, the tag question should be always 'isn't it'.
Isn't it would require some antecedent for "it" that does not exist in some of these examples. If you mean, "Isn't it the case that this is true or applicable?", you'd need to expound at least a little, saying isn't it so?. Equivalent, colloquial tag questions with the same basic meaning here are right?, eh?, huh? You could say, Waste not, want not, right?
If you wanted, you could construct a tag question that agrees with the actual content of the proverb. As you suspect, since the proverb is a set phrase, the generic tag question would be better. Still, you could, if you really wanted, say "None is none under the sun, isn't it?" and "Time and tide wait for no man, don't they?" Since waste not, want not is in a command form, I don't think there is any good way to add a tag question that agrees grammatically with the content.
Problem 2: What is the correct tag question of interrogative sentences like: (a) Who cares, do they?
"Who cares, do they?" sounds like wordplay. It isn't a suitable tag question.
Since Who cares? is a common rhetorical question, it makes sense to tag it generically, as in, "Who cares, right?"
If it were a real interrogative question, no substantive tag would apply. You would not say, "What is her number, right?" nor "What is her number, is it?" These are not grammatical.
In colloquial speech, some speakers might add a hunh, eh, hmm, or similar at the end of some interrogative questions. I don't recommend trying to adopt this practice.
Problem 3:Can we add tag question to phrases like (a) Good morning, ......? (b) Happy birthday, ....?
Not as such. I don't understand what this would do.
With good morning, you could certainly ask the question, "Good morning, isn't it?" or "Good morning, wouldn't you say?" or "Good morning, I hope?" Though these start with a clause good morning, I would not consider that clause to be equivalent to the greeting good morning, per se.
Happy birthday is less suitable to such twisting around.
Best Answer
This is called hypophora. It's a common type of rhetorical question.
Technically, that is what the question is called. The answer is apparently called anthyphophora. You can check out some examples of it here; one of the examples is very similar to what you've quoted. That link also includes a definition.