Can the word "THIS" be a dummy subject? For example: "This is CNN". or "Hi, This is John (on the phone?)

Question

The following is from a dialogue between mother and an officer of the Health Insurance Commission (HIC). It is about the Australian Immunisation Register.

HIC Officer: Good afternoon. I’m David Hutton. I understand you have some questions about a letter you received from us concerning immunisation. Is this your daughter?

Mother: Actually, it is my son, he is 17 months old. I thought all necessary vaccinations are already done, so I was surprised when I received the immunization letter.

The use of "this" in the question "Is this your daughter?" is interesting, because "THIS" might act as a dummy subject like "IT" or "THERE". For instance, when we say on the phone "Hi, this is John", "THIS" is not actually pointing at a physical person. Or when we say "This is CNN", it is not actually pointing at something or someone or somewhere.

Likewise, the sentence "IS THIS YOUR DAUGHTER?" may not definitely be pointing at a baby at the time of speaking.

The officer migth not be pointing at a physical person who was there at the time speaking, but he might have talked about the vaccination of the mother's possible baby in his imagination.

So, the officer when said "is this your daughter?" he might not be pointing at a real baby at the time of speaking.

Is my conclusion right or does the sentence "Is this your daughter?" definitely mean the baby was there at the time of speaking and the officer was pointing at him/her by saying "THIS"?

Answer 1

I think the "dummy subject"you are talking about is that which is known as an expletive subject. A good example is It is raining.

In the text you quote I don't believe this is used in quite the same way. Even though there is no this at whom one could point, it could refer to a person named in the letter from David Hutton. Or if not a named person, it seems to refer to an identifiable person. And that's also the case when I say Is this your daughter. There has to be a definite person, about whom I am inquiring.

That is not quite the same as saying It is raining. Because in that instance it is impossible to point, either literally or figuratively at the thing called it. Indeed it does not represent anything.

This is CNN is surely saying to us - the thing you are looking at is CNN. Again it is not quite the same as It is sunny outdoors. It is quite impossible in the case of a so-called expletive subject to say what it is.

I cannot think of an example of this used in quite that way.