Today we were learning defining and non-defining relative clauses in a class, e.g. using this exercise:

Defining and non-defining relative clauses exercise

The rule seems to be relatively clear:

  1. If there are commas, then we are talking about all subjects, not some specific one, and this is a non-defining clause;
  2. If there are no commas, then we are talking about some of many and this is defining clause.

What am I wondering about is that, when someone uses these clauses they put some additional information into it. Let us consider an example with sister:

(1) If I write

My sister, who lives in LA, is a designer.

then I also add info, that I have only one sister.

(2) If I use

My sister who lives in LA is a designer.

then I also add info, that I have many sisters.

However, maybe I am chatting in a public group and I do not want to disclosure a number of my relatives. I just want to say, that I have a sister, she is a designer, she also lives in LA and maybe she could help, that's all!

In this case if I have two sisters and write (1), then I will lie; if I write (2), then I will disclosure this additional info, which I wouldn't. Therefore, if I want to be concise, then it seems that language somehow defines how I share additional information with others and how honest I am!

Sorry, if this is a completely stupid question, but it drives me crazy, since there are no such clauses in my native language. So here I want to hear from native speakers about the subject. How do you use these clauses in your daily routine? How would you write in the example with sister above?

P.S. I know that there several questions with ~the same title, but this one is not about grammar and some specific case.


1 Answer 1


If you want to say that you have a sister without saying anything more about other sisters: I have a sister

If you want to say this sister is in Los Angeles: I have a sister in Los Angeles

... and she's a designer: I have a sister in Los Angeles who is a designer

... and maybe she could help: I have a sister in Los Angeles who is a designer, perhaps she could help

To any of these, someone might ask whether you have any more brothers and sisters.

  • Thank you for the answer, but 'who is a designer' in your examples seems to be the same defining relative clause (or non- if we use commas), so we are stuck in the same place, doesn't it? Anyway, I guess Jason answered my question well, though I will be glad to read other opinions
    – ololobus
    Jul 18, 2019 at 9:02
  • 1
    The real way these are understood is by context, sense, and emphasis. In your examples we won't be sure if you have any more sisters: substitute "friend" for "sister", with and without commas, and it's clearly one-of-several. Substitute "father" and it's clearly unique. In your sentence b, it might be defining against "my friend who lives in LA" rather than "my sister(s) who don't live in LA". The "I have a ..." construction explicitly makes "is a designer" non-defining because the main verb is now "have".
    – jonathanjo
    Jul 18, 2019 at 9:56

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