(Native speaker of American English here.)
artart wrote:1) I am talking about the Harry who works at the hospital not the one who works at the library.
2) I am talking about Harry who works at the hospital not the one who works at the library.
3) I am talking about the Harry at the hospital not the one at the library.
4) I am talking about Harry at the hospital not the one at the library.
5) Harry at the hospital told me that, not the one who works at the library.
6) Harry, at the hospital, told me that, not the one who works at the library.
Which of the above are grammatical and meaningful?
Which are idiomatic?
They all sound grammatical and unambiguously meaningful to me. (There are two persons named Harry--one at the hospital and one at the library--both known to the listener, and in all cases the speaker is specifying they're talking about person named Harry who works or is at the hospital.)
Stylistically, (1) sounds better than (2) and (3) than (4), both for the same reason (parallel structure), but none of these sentences sounds unidiomatic. (5) is better than (6), since "at the hospital" is restrictive, not incidental. But I don't perceive any difference in meaning between the sentences; (6) just looks like it was written by someone who doesn't understand prescriptive comma usage in English.
"Richmond is a real scholar; Owen just learns languages because he can't bear not to know what other people are saying."--Margaret Lattimore on her two sons