Struggle determining which relative clause has extra information

Question

Preliminary

Based on my book, there are two types of relative clauses: "The relative clauses that tell you which person or thing (or what kind of person or thing) the speaker means" and "The relative clause that don't tell you which person or thing the speaker means and give us extra infornation". From now on, let's call them as type 1 and type 2 respectively.

These are examples given by my book:

Type 1

• The woman who lives next door to me is a doctor.

• Grace works for a company that makes furniture.

• We stayed at the hotel (that) you recommended.

With those clauses, commas (,) are not used. You can use that. (Who/which/that)

Type 2

• My brother Ben, who lives in Hong Kong, is an architect.

• Anna told me about her new job, which she's enjoying a lot.

• We stayed at the Park Hotel, which a friend of ours recommended.

Those relative clauses use commas (,). You cannot use that. (who/which)

Question

At first, I thought when the speaker mentions the specific name of a person or a building, it's the relative clause type 2. However, I seem to be wrong, look at these examples I took from my book:

Correct them and put commas where necessary. Write 'OK' if the sentence is correct.

1. My office that is on the second floor is very small.

My answer:

• OK

Reason:

Since there's no specific name, I'm assuming it's type 1. For instance, I have 3 offices and by describing one of them as in 1) I don't think it gives me extra information.

Key answer: (turned out to be type 2)

My office, which is on the second floor, is very small.

2. The sun that is one of millions of stars in the universe provides us with heat and light.

My answer:

• OK

Reason:

Assuming using that isn't a problem.

Key answer: (turned out to be type 2)

The sun, which is one of millions of stars in the universe, provides us with heat and light.

As given in example 2, if the thing is clear (there is only one sun), is it automatically type 2? And why can't I use that on both 1) and 2)? Hope you will also tell me another difference between type 1 and type 2. Thanks!

Answer 1

General Rules

Defining relative clauses ("type 1") identify the noun, so, without the relative clause, it wouldn't be clear which noun you're referring to. This type of relative clause is part of the noun itself.

Non-defining relative clauses ("type 2") don't help you identify which noun you're speaking about. This type of relative clause is like a second sentence about the same noun.

Your examples

1. [My office], which is on the second floor, is very small.

You normally only have one office, so the relative clause doesn't clarify which office you mean. The phrase in brackets [] is the entire noun. This could be broken down into two independent sentences, My office is on the second floor, and My office is very small without losing any meaning.

2. [The sun], which is one of millions of stars in the universe, provides us with heat and light.

There is only one star called "the sun", so the relative clause isn't necessary to identify which sun you mean. I can break this into two sentences as well: The sun is one of millions of starts in the universe and The sun provides us with heat and light.

My examples

3. [My office that's on the second floor] is smaller than my other one on the 5th floor.

Here, I have two offices, so the relative clause is required to identify which office, and the phrase in brackets is the whole noun. If you try to break this into two sentences about "my office", one of them is nonsense:

*My office is smaller than my other one on the 5th floor.

4. [The sun that's in the sky] doesn't burn as bright as [the sun that's in my heart].

Here, I'm comparing two suns. Even though one of them is metaphorical, the relative clauses are required to distinguish the two "suns".

5. [My nephew who is an electrician] is a fantastic hockey player.

I have three nephews, so the relative clause is required for you to know which of my nephews I'm talking about. The phrase in brackets is the whole noun, including the relative clause. While the sentence, My nephew is a fantastic hockey player makes sense, if you know I have three nephews, you still don't know which one I'm talking about.

6. [My niece], who loves horses, is a children's camp director.

I only have one niece, so the relative clause isn't necessary for you to know which niece I'm talking about. The noun phrase in brackets is the whole noun. The relative clause tells you she likes horses, and the main clause tells you she's a camp director.

It's important to notice here that the type of noun doesn't determine which type of relative clause is correct. The only important factor is whether the clause is required for the audience to understand which noun you're talking about.