A couple of days ago, Jim Bisso sent me a question:
I've been embattled by a bunch of peevologists over the grammaticality of sentences of the sort: "my mother(,) she is a good person". I have pointed out that many kinds of apposition are not only acceptable but flow from the pens of some of our finest writers, but they are having none of that. Somehow a construction like "we the people of the United States etc." is okay, but reverse the order of Pron + NP to NP + Pron and sparks start to fly. I say it's simply a stylistic matter and not a syntactic one, but who am I? What say you? (Do you know any monographs that I might delve into to fuel my argument?)
Executive summary: This construction goes back to Old English, and is still widely used in spoken English and in some regional varieties ; but its use in formal written English has been decreasing since about 1500, and is now either informal or archaic.
If I understand what Jim has in mind, the sentences at issue are not really appositives. In nominal appositives, a noun phrase is followed by another noun phrase that provides additional information about it, so to speak in parallel. Appositives are common in news writing — the lead sentence of the first article I picked in this morning NYT has two of them (indicated in boldface):
Warren E. Buffett, the country’s most famous investor and one of the world’s richest men, announced on Tuesday that he would invest $5 billion in Goldman Sachs, the embattled Wall Street titan, in a move that could bolster confidence in the financial markets.
Appositives used after third-person pronouns are usually editorial interpolations to clarify the reference ("They (the defense) got to the line and showed their hand"), since there's otherwise little reason not to use the appositive phrase in place of the pronoun. With first and second person pronouns — as in "we the people" — the situation is obviously different.
Jim's sentence ("my mother, she is a good person") is an example of a different construction, where a non-vocative noun phrase in initial position is set off from a following sentence that contains one or more pronouns coreferential with the initial NP. Since Haj Ross's 1967 dissertation Constraints on Variables in Syntax, this construction has been known as "left dislocation". Haj's examples (pp. 422-451) included:
The man my father works with in Boston, he's going to tell the police that the traffic expert has set that traffic light on the corner of Murk Street far too low.
My father, he's Armenian, and my mother, she's Greek.
My wife, somebody stole her handbag last night.
When the pronoun is sentence-initial, you might think that it's in apposition with the left-dislocated noun phrase. But this generally makes neither semantic nor prosodic sense. If the structure were really
My father - he - 's Armenian.
the phrasing would be different (and strange), and it's hard to see why one would want to add the pronoun, which would add none of the parallel information that appositives usually do.
And the third example ("My wife, somebody stole her handbag last night") illustrates the fact that the pronoun need not be adjacent to the left-dislocated noun at all. (Though examples with the pronoun in subject position are by far the commonest.)
Constructions of this general type are common across the languages of the world, and in so-called topic-prominent languages, they're the norm. The left-dislocation structure is often said to divide the sentence into topic and comment, or some similar sort of articulation of information. (This works when the initial item is a full noun phrase, referenced in the following sentence by a pronoun or pronouns, but it wouldn't work the other way around. There's a lot more to said about the pragmatics of LD, and there's a large literature discussing it, but I'll leave it there for now.)
Elizabeth Traugott ("Old English left-dislocations: Their structure and information status", Folia Linguistica. 41(3-4): 405–441, 2007) gives examples like this from Old English:
Se awyrigeda deofol syððan he ðone frumsceapenan man beswac.
syððan he hæfde anweald ofer ungelyfedum mannum.
that cursed devil after he that first-created man deceived
afterwards he had control over unbelieving men
In a corpus search, she found "a total of 280 left-dislocated main clauses, out of 39,654 main clauses (0.7%), and a total of 53 left-dislocated subordinate clauses out of a total of 34,866 subordinate clauses (0.15%)".
This rate appears to decrease through the history of (written) English. Javier Pérez Guerra & David Tizón-Couto, "‘These hands, they are apt enough to dislocate and tear thy flesh’: On Left Dislocation in the Recent History of the English Language", 2004, give counts of left-dislocations per 1,000 words in a corpus study of late Middle English, early Modern English (16th-17th century), late Modern English (18th century), and Present-Day English (20th century):
Unfortunately, Traugott doesn't give word-count information for the material she searched, but she does list the works, and by reference to the original corpus documentation I tentatively estimate the total as about 458,000 words, which would yield a left-dislocation rate of about 0.72 per 1,000 words. Whether or not this is accurate, it seems likely that the LD rate in Old English was higher than the historical estimates for texts since 1500.
In the earlier materials, left dislocation is found in formal prose as well as in less formal contexts such as letters. In fact, Pérez Guerra and Tizón-Couto argue that "LD cannot be characterised as a strategy applying to exclusively informal language since most of the corpus examples are found in instructive and narrative text types, which clearly instantiate formal English". This argument is not as compelling for their present-day English sample, which comes from the LOB corpus, where the narrative texts include several genres that are likely to be written in a quasi-conversational style, even leaving aside the high proportion of dialogue (mysteries, science fiction, westerns, romance).
Within the past century or so, LD has clearly remained a lively part of spoken English. According to Michelle Gregory and Laura Michaelis ("Topicalization and left-dislocation: a functional opposition revisited", J. Pragmatics 33(11): 1665-1706, 2001), searching part of the Switchboard corpus, found 187 instances of LD in 32,805 statements and questions, for a rate of 0.6%, which is not very different from the rate of 0.7% that Traugott found for LD in main clauses in Old English.
They give examples like
The Saturns, you can get air bags in them.
And heavy metal, it's noisy.
Well, my car, it's an eighty six.
However, the use of LD in formal written English has become quite rare over the past century or so. Even in poetry, examples tend to occur in consciously archaic writing, e.g. Walter de la Mare, "The Cage":
Fret now no more; be still. Those steadfast eyes,
Those folded hands, they cannot set you free;
Only with beauty wake wild memories—
Sorrow for where you are, for where you would be.
Or in regional varieties of English, e.g. Hugh McDiarmid, "To Circumjack Cencrastus" (1930):
My love she is the hardest thocht
That ony brain can ha'e,
And there is nocht worth ha'en in life
That doesna lead her way.
Or in quoted speech, e.g. Robinson Jeffers, "The Loving Shepherdess" (1928):
Fern lagged and lagged,
Dibbling the dust with the mere points of the hoof
Of the hurt fore-leg, and rolling up to her shepherdess
The ache of reproachful eyes. "Oh Fern, Oh Fern,
What can I do? I'm not a man, to be able to carry you.
My father, he could have carried you." Tears from Clare's eyes
Fell in the roadway; she was always either joyful or weeping.
Examples in contemporary news text are almost always in quotes or in informal passages of opinion pieces. Even in the 18th century, my impression is that LD is commoner in e.g. first-person narratives than in more formal expository prose. Thus Jane Barker, Exilius (1719):
Valerius, though a little Opposite at first, yet, upon his Mother’s pressing, and repeating how far my Happiness was the Object, if not the whole End of the Undertaking, he at last consented, and this my forced Marriage was resolv'd on that coming Day.
And I just read 400 sentences of Gibbon's Decline and Fall without finding any examples of LD — this suggests that he used this construction at a rate lower than the 1 in 175 that Gregory and Michaelis found for contemporary American English conversational speech.
So I'd answer Jim's question as follows. Left dislocation is certainly grammatical in English. Up to 1500 or so, roughly one in every 100 or 200 sentences had this form, even in formal writing, and a similar frequency of use continues in spoken English to this day. Over the past few centuries, the frequency of this construction in standard written English has been declining, and it's now quite rare except in archaic styles, in representations of speech, or in informal styles that use spoken-language norms. Therefore Jim's claim that the issue is one of style rather than grammaticality is correct, although his identification of LD as a form of apposition is misleading, as is his citation of "we the people …" as a relevant example.