Thank you jutfrank.
I'm not sure what you mean by 'real' but proper nouns by no means have to refer to concrete things. Any name of any kind of organisation or company or institution, for example, is non-concrete. These things are very much conceptual. (We have to be careful how we define 'concept'.)
---I should have made a precise definition of "concept" and "proper noun".
Merriam-Webster's definition of a proper noun is: a noun that designates a particular being or thing, does not take a limiting modifier, and is usually capitalized in English.
And its definition of a concept is: an abstract or generic idea generalized from particular instances.
You said: any name of any kind of organisation or company or institution, for example, is non-concrete. That's right, but I had in mind the words like "John Smith" and "Paris".
The word "John Smith" is created to refer to the only person in the world socially recognised by the name. Here it is assumed there is no other "John Smith", so "John Smith" isn't a concept.
As for "a real and concrete thing", I didn't use it well. My expression was far from being satisfactory. I meant it as being contrary to a concept, that is; being substantial.
Concepts can be used in sentences and discourses when suitable determiners are added to them. Say, in the case of "book", a book or books or book with a certain determiner is used as a substantial thing. A book or books or book with a certain determiner I meant by "a real and concrete book".
"John Smith" isn't a concept, and can be used in sentences and discourses without any determiner. So with "Paris".
On the other hand, as you say, any name of any kind of organisation or company or institution, for example, is non-concrete, which I agree with you.
But the meaning of "concrete" is different from mine.
Some proper nouns need determiners (such as definite articles) and some do not.
---Do you mean some proper nouns work as common nouns? Is it an expanded functionality of proper nouns?
Can't I say things which need determiners are all concepts?
(That's my greatest concern.)
I doubt it. That (a beautiful Paris) would be extremely odd and unusual usage.
---I've seen similar phrases in catchphrases travel agencies in Japan created, but I agree with you in that it's odd and unusual. So how about "a Paris we hadn't imagined" or "the Paris in 1966"? Still odd and unusual?
I don't know if it's possible to assume plural Parises. I think it's also possible there is only one Paris in the world, and people see Paris from different angles or have different impressions about Paris, in which case there are no plural Parises in the world.
If you approve of plural Parises, I think you have to say Paris is a common noun.
Or do you need to still call Paris in such cases a proper noun for convenience, although it has lost the implicit message that Paris is the only thing in the world?
As for "John Smith", I've seen a sentence like "A John Smith came to see you.".
Probably "a John Smith" here means a person called John Smith. Here there are plural John Smiths.
In unusual cases such as this, the speaker is treating what is normally considered a proper noun (here the word Jane) as if it were a common noun. It sounds odd precisely because of this.
---Do you mean that "Jane" (as well as "Paris") isn't a common name?
Also, we call it London Bridge with no article.
---That's why I'm a bit confused with the London bridge.
I surmise some Londoners called a newly built bridge by that name, probably because they wanted to claim the new bridge, not the old London Bridge, is authentic and suitable enough to be called by that name. (of course it's just my surmise)
London Bridge and the London Bridge are 2 different things. It's not just that there are 2 London bridges, unlike plural Parises (?) above mentioned. So I think it can be said both 2 are definitely common nouns.
Can I say after all, that when an indefinite article is added to a proper noun, it functions as if it were a common noun, and when a definite article is added, it functions as a common noun? Am I right? I'm a bit confused, sorry. Proper nouns are difficult for me to understand. I'm sorry for holding you up so long.