just to make doubly sure:

it's "a ghrá geal" and not "a ghrá gheal," correct?

A ghrá ghil!

Yes, "a ghrá ghil" -> the adjective has to be in the vocative too.

I am wondering now about the vocative vs the possessive. What about: mo ghrá geal?

In Welsh studies, the term "contact mutation" is used when the lenition is triggered solely by the presence or absence of a particular preceding element with no other grammatical considerations coming into play. I think such a term is useful here. Lenition after mo is a contact mutation. It doesn't matter what the case, gender, number, etc. of the noun is; if it follows mo, then it is lenited. (Contrast this to an, where the presence or absence of lenition or eclipsis is completely subject to grammatical considerations.)

"A ghrá geal" and "a ghrá ghil" are both correct - depends whether the vocative is understood literally or metaphorically.

I'd plump for "a ghrá geal" myself but you will hear them both, and both are correct.

quote:

I am wondering now about the vocative vs the possessive. What about: mo ghrá geal?

Normally you don't use possessives with the vocative.

Aibí > can love be expressed metaphorically? For taiscidh, stór etc, I see, but for "love"... ? What can "love" mean, except "love" ?

Does the rule rely on metaphoricality per se or simply animacy? Moreover, is there really that principled a distinction between the metaphoricality of "valued object" > "beloved person" and the metonymy of "love" > "beloved person"?

Lughaidh, "is mo ghrá geal thu" - it doesn't have to be vocative.

Abigail is talking about a "rule" where non-animate nouns applied to people don't take the vocative eg "a rún", "a stór" -actually IWM does refer to "a rúin" in one paragraph. I wonder whether this rule has crept in over the last century due to the decline of the vocative? The old green Christian Brothers' Grammar showed a full complement of vocatives for every noun, including non-animates....