This construction is common in speech, and in writing which emulates speech.
The initial noun phrase acts as a discourse marker to announce a shift of focus to a new or resumed topic; it will usually be emphasized with stress, pitch, and prosody—often a falling pitch similar to 'comma intonation' or rising pitch similar to 'question intonation'.
In writing it should be followed by some sort of disjunctive point, such as a comma, dash, question mark or colon.
Most of them are my brothers, but John, he's my husband.
The construction is perfectly grammatical, but it is rarely used in formal writing, which lacks the accompanying vocal resources.
Formal writing has other methods for achieving the same marking: Most of them are my brothers; John, however , is my husband.
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As the sentences stand, the pronouns are normally redundant however, there are some circumstances where you would use it with some modifications in punctuation.
The first is in poetic usage where the extra pronoun is used either as a matter of form (this construction is common in folk music) or to preserve metre, e.g:
Mary
she went to the store For to meet with the man she adored
And she watched by the hour
While he measured out flour And loitered around by the door Fol a diddle de roll, etc.
Another common construction is in response to a question.
For example: Q: Who is this John you keep mentioning?
A: John?
He's my husband.
So overall it is not how native English speakers would usually construct a sentence in casual conversation or writing but
neither is it wrong nor particularly inelegant.
ell.stackexchange.com/users/32210/Chris Johns
Yes, but you are punctuating the sentence improperly.
To record this kind of phrase in English, we use the em-dash to set the appositive apart from the rest of the sentence.
This gives: John— he's my husband— [rest of sentence].
Mary— she went to the store— [rest of sentence].
We use the em-dash to separate the appositive here, as opposed to the more typical comma, because the appositive phrase is an independent clause.
You could reword the sentences as follows to make the comma fit in.
John, my husband, [rest of sentence].
Mary, who went to the store, [rest of sentence].
That said, both formats are grammatically correct and indeed common in spoken English.
The emdash is often represented in written English in keyboard-recorded media via the digraph '--', rather than the more traditional character '—'
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The construction is called "left-dislocation topicalization".
Here's a paper 1 about the phenomenon, which defines the term in the introduction:
In this paper, I will investigate the information-structural properties of two English structures which utilize word-order variation for such purposes.
(1a) and (1b) provide examples for the constructions.
(1) a. Tom, I like.
b. Tom, I like him.
The common name in the literature for the configuration in (1a) is "Topicalization" (abbreviated as TOP henceforth), while (1b) is most commonly called "Left-Dislocation" (abbreviated as LD).
[1]
On English Topicalization and Left-Dislocation from an Information-Structural Perspective, by Péter Szűcs
ell.stackexchange.com/users/30611/Charlie
This is common in informal English.
You add extra information about the person you have just mentioned.
As StoneyB marked in his answer such extra information can be " emphasized with stress, pitch, and prosody ": John, he's my husband, has just gone to the shop.
Henry, oh, he's working in the garage.
Oh, come on, that George of yours, he isn't a nice person.
Depending on what punctuation mark is placed the meaning is different.
Mary?
She went to the store.
John!
You naughty kid!
Get here immediately!
ell.stackexchange.com/users/44134/SovereignSun
Is it correct English to write “John he is my husband,” or, “Mary she went to the store?”  I hear this construction  frequently from TV and Radio Journalists. Is there a name for this construction?
Is it correct English to write "John he is my husband," or, "Mary she went to the store?"
ell.stackexchange.com
<word-order>
ell.stackexchange.com/questions/132899
ell.stackexchange.com/users/57026/rwhissen
This can be used with the correct punctuation. Em-dashes are used as follows: "John— he's my husband— [rest of sentence]". Alternatively, sentences can be rewritten with commas, as in: "Mary, who went to the store, [rest of sentence]." Both formats are grammatically correct and common in spoken English. You're correct, but you're punctuating the sentence incorrectly.
You're correct, but you're punctuating the sentence incorrectly. In English, we use the em-dash to separate the appositive from the rest of the sentence. To make the comma fit in, rewrite the sentences as follows. This yields: John— he's my husband— [continued]. Mary— she went shopping— [end of sentence]