Woodcock translates est mihi magna domus as “there is to me a large house” (A New Latin Syntax, 46).
He goes on to specifically makes a point about the verb “to be” in the dative of possession, stating that
The verb ‘to be’ asserts the existence of the thing possessed as not being previously known. This use of the dative is common at all periods and in all types of Latin. The dative thus used differs from a predicated Genitive of possession or from a possessive adjective, for > Illius duae fuere filiae > would mean ‘The two daughters were his and > Est mea magna domus > would mean ‘The large house is mine,’ implying that the existence of the thing possessed is already known.
All well and good, and he certainly isn’t the only one to understand the literal Latin as using an impersonal form of the verb esse (see A and G below).
However, Pinkster, in his Oxford Latin Syntax, p. 164 (which I don’t have, and I’m relying on limited previews) specifically states that liber in est mihi liber is the subject, not a predicate, that is, that the literal translation is “a book is to me.”
This translation does not assert “the existence of the thing possessed as not being previously known,” as Woodcock argued.
Whether the dative of possession is translated with an impersonal form of sum or not seems to be hit and miss in the grammar books. Allen and Greenough, for example, use the impersonal:
Est mihi domī pater (Ecl. 3.33)
I have a father at home.
(> there is to me> )
However, they do not follow Woodcock’s view that an assertion is being made as to something’s existence. Instead, they distinguish this use from the possessive by stating it emphasizes ownership:
Note— The genitive or a possessive with > esse > emphasizes the > possessor> ; the dative, the fact of possession.
Liber est meus.
The book is MINE (and no one’s else).Est mihi liber.
I HAVE a book (among other things).
So who is right?
I do like Woodcock’s succinct definition of the dative of possession (and sympathetic dative, which Pinkster also deals with, though I cannot preview this section unfortunately), but I’m not sure how to resolve these issues.