When not to use existential 'there'?

Question

Some dictionaries and grammar books in my language give funny restrictions for "There is ~" structure.

A newer grammar book changed a little and now says it's ok to use "There is(are) ~" for proper nouns as long as it's a new theme. Before they said that only when put up several names in a row it's ok to use the structure for proper nouns or nouns led by 'the'.

Those books and dictionaries say "There is" is to bring up a new theme and so use of 'the' is limited to where grammatically needed case such as with a superlative adjective or followed by a modifier like a relative pronoun or an of-clause.

But I've learned here (and there) that it's not actually right.

I wonder why those books and dictionaries in my language are like that.

I wonder if it's ok to say "Is there Mr. Smith here today?"

[edit to add] An example I found on Google is clearly not a new theme:

e.g. There's the girl I was talking about.（The New Cambridge English Course 3 Teacher's Book, 1992）

[edit to add]
It's been a while, but now I think I can summarize it. When a thing or two you know come to your mind as relevant items to an idea, you can say "There's the ... and the ...", but when you ask a question, "Is there ...?" is an expression to ask if something ever exist or not, so it's not grammatical and sounds strange if it's used to ask if one of the staff is present today. (Nov. 27, 2016)

Answer 1

Context is, once again, the important factor!

It's important to distinguish between the existential there, and the simple adverbial use (Where is the ball? The ball is there.)

Let's have a look at your example sentence:

There's the girl I was talking about.

Now, this sentence can mean two different things. Without context, we cannot tell which of the two is meant. It can be simple adverbial use:

We are talking, possibly about a girl, when a girl enters the room.
“There is the girl I was talking about!”

In this case there is not an existential where, it simply indicates the position of the girl: she is there, walking through the door.

Now, the same sentence could be existential:

I am giving you a list of important people in my life: my family, my best friend, oh, and
“There is the girl I was talking about.”

Now, I wasn't just now talking about that girl! I have been talking about that girl at some earlier occasion, but right now I was talking about a different subject. So in context, that girl is a new theme!

Now, let's have a look at your other sentence:

*Is there Mr. Smith here today?

This sentence is not grammatical. The question is: what do you want to ask? Let's suppose you are at a reception desk at a company, and you are looking for a specific Mr. Smith — you want to talk to him. You [i]know[/] that he exists, so there is now reason to inquire about his existence! You just want to know whether he is present or not:

Is Mr. Smith here today?

You can even use there, for instance when you are not on the premises (let's assume you ask for him by phone):

Is Mr. Smith there?

Keep in mind that in that last sentence, there is simply adverbial, not existential!

Now, you could use the existential there, if you actually are not sure whether Mr. Smith exists:

Is there a Mr. Smith working here?

Notice that you are not asking about the Mr. Smith, you are asking if there is any person by the name of Mr. Smith. Obviously, you are introducing a new theme here. Even if you have been talking about the Mr. Smith you are looking for, you can use this:

I was told to bring this package to Mr. Smith, but I don't know where he works. Is there a Mr. Smith working at this company?

It seems that the second Mr. Smith is not a “new theme”, but actually, it is. The first Mr. Smith is a specific Mr. Smith I should deliver a package to, the second Mr. Smith is a hypothetical Mr. Smith that may or may not exist. I am implying that they may be the same people, but I cannot assume that — I'm not even sure if that second Mr. Smith exists!