Commas around part of a sentence often signal that the element is not essential to the meaning of the sentence: Nonessential element: e.g. The company, which is located in Oklahoma, has a good reputation. This nonessential element may modify or rename the word it refers to (company in the example), but it does not limit the word to a particular individual or group (Because it does not restricct meaning.) Non-essential elements are not essential,but punctuation is. I don't understand why "which is located in Oklahoma" is nonessential, why " it does not limit the word to a particular individual or group"? I think it is essential, because it tells you what company has a good reputation? A company which is located in Oklahoma. In contrast, an essential element does limit the word it refers to: Essential element e.g. The company rewards employees who work hard. In this example the underlined essential element cannot be omitted withouot leaving the meaning of employees too general. Because it is essential, such an element is not set off with commas. So here, Assuredly is that: "who work hard" must be essential , because it tells you who are the employees that the company rewards: Hard working. So i really can't figure out what is unessential element, i think most of time, all the elements are essential.

THanks for replies.
Full Member227
I don't know how many grammar books I have read without encountering the term you use, 'nonessential element'. Here are some examples of relative clauses without fancy terms. Pay attention to the possible pronouns and commas.

He has a son, who lives in Tokyo.
- He has only one son and he lives in Tokyo.

He has a son who/that lives in Tokyo.
- He has at least two sons, one of whom lives in Tokyo. We are not told anything about his other son(s).

He has sons, who live in Tokyo.
- He has at least two sons, perhaps more, and all his sons live in Tokyo.

He has sons who/that live in Tokyo.
- Not all of his sons live in Tokyo, at least two of them do, though.

I have a pen, which doesn't work.
- I have only one pen and it doesn't work.

I have a pen that/which doesn't work.
- I have at least two pens and one of them doesn't work.

The sailors, who lost their lives, were young.
- All the sailors lost their lives and were of course young.

The sailors who/that lost their lives were young.
- Not all sailors lost their lives but those who did were all young. We are not told anything about the age of the sailors who survived the accident.

Cheers
CB
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«He has a son who/that lives in Tokyo.
- He has at least two sons, one of whom lives in Tokyo. We are not told anything about his other son(s).»

Are you sure he has at least two sons? I'd say at least one...

Ex. 1: «...The company, which is located in Oklahoma, has a good reputation.»
We have already introduced that company and thus limited the meaning of that particular entry of the word «company» to the one we have reffered to in the previous sentence. The informatin about its location is additional: it doesn't apply further limits to the meaning of the word, it just declares some statement about the already-defined object.

«I don't understand why "which is located in Oklahoma" is nonessential, why "it does not limit the word to a particular individual or group"?»

Because the meaning of the word have already been limited in the previous text, for example:

«This is the phone number of a car-saling company. The company, which..., ...».

Here we restrict the meaning of «company» in the first sentence, and, then, use the word with this restricted meaning in the second, giving additional information about the defined object (some speacial meaning)

«I think it is essential, because it tells you what company has a good reputation?»

«Essential» is just a grammatical term here. Read it as «essential for the identification» of the word it applies to. It's in no way what we mean by just «essential» in everyday life.

Ex. 2: «The company rewards employees who work hard.»

Analogously. The «employees» means literally any employee. But the comany rewards only part of them. So, we restrict the word «employees» to the multiplicity of ones with a certain property: the ones who work hard. It's not additional info, because this clause changes (namely, restricts) the possible multiplicity of its meaning to one of its subsets.

The operation is called «constraint» (!) in the theory of relations.
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