THanks for replies.
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.
- 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.
People are waiting to help.
Related forum topics: