The so called “Dative of Possession” (Crosby and Schaeffer pg. 16) according to classics.osu.edu:
The Dative case is chiefly used to indicate the person for whom (that is, f> or whose advantage or disadvantage> ) an action happens or a quality exists. In a sense, all datives are Datives of Reference or Datives of Advantage and Disadvantage; as a result that particular category is not very useful though it does remind that the Dative case refers to a personal or affective interest in the action. The most useful and common translation of the dative case into English is with the preposition “for”. Our sense that the dative is to be translated with the preposition “to” is a result of the common use of the dative with a verb of giving where the English idiom is “I give this to you.” However, even with the indirect object you can see how “for” is the basic sense if you imagine someone handing you a book and saying “For you.”
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Dative of Possession: > The dative is used with the verb “to be” to indicate the person > for whose benefit something exists> . In many cases, this implies possession. The Dative, however, is different from the Genitive of possession in that it typically implies a personal connection of use, enjoyment, etc. that goes beyond the legal possession. For this reason, sometimes this dative is called the “sympathetic dative”.
https://classics.osu.edu/Undergraduate-Studies/Latin-Program/Grammar/Cases/dative-case
FOR ANYONE WITH ACCESS TO YOUTUBE: Dative of Possession tutorial
https://www.youtube.com/watch?v=_mTBPC_oYsE
apparently we had a short discussion of this topic Dative of Possession five years ago.
http://discourse.textkit.com/t/dative-of-possession/11564/1
and a paper on it
M. C. BENVENUTO - F. POMPEO, Expressions of predicative possession
in Ancient Greek: “εἶναι plus dative” and “εἶναι plus genitive” constructions
From the introduction, the rules for the sample to be studied, note the text in italics in reference to Joel’s assessment "Neither one is the “Dative of Possession” (pg. 16). Both are “Dative with Adjectives” .
In order to highlight specific features of the two constructions,
having read the texts in their entirety, we established the formal and
functional criteria for the selection of the material to be investigated.
First of all, ambiguous occurrences were excluded. Secondly, we left
out all instances of predicative possession with any verb other than
the simple εἶναι. Subsequently, only two-constituent constructions,
such as “subject εἶναι dative” and “subject εἶναι genitive” were
considered. We thus omitted sentences with a form of the verb εἶναι
and three nominal items, such as Δαρείῳ, ἱπποκόμος and νήρ in (3),
as well as occurrences > where the dative can depend on an adjective> , a
participle or a verbal adjective