JK Rowling pens a Harry Potter prequel / War of Roses/Holmes?Figg/Walpurga

[Carol]

CJ:
> It lost the morphological distinctions;

Carol responds:
Right.

CJ:
> and yet grammarians continued to distinguish accusative and dative
cases long after the morphological distinctives had disappeared (the
subsumption of the two into a single "objective case" is a 20th
century phenomenon still not universally followed). I think there are
two possible explanations. Either they were simply hadn't gotten
around to jettisoning older terminology, or they genuinely still found
the cases useful, any lack of morphological distinction notwithstanding.

Carol responds:
In the case of nominative for subjective, I think you're correct. My
ancient copy of "The Plain English Handbook" (copyright 1966!) give
the pronoun cases as nominative, objective, and possessive. I was
never, as a student of English in high school, college, or graduate
school, exposed to the terms genitive, dative, or accusative in
relation to English (except for Anglo-Saxon). They were, however, used
(along with ablative) for Latin.

I think possibly the problem, as you perceive it, is that so few 
students now take Latin (and virtually none take Anglo-Saxon below the
college level), so the term objective case has come to be used almost
universally, in the U.S. at least, for all types of objects in
English. My Plain English Handbook (intended, if you're not familiar
with it, as an aid to grammar and composition for high school
students) gives the following list of uses for the objective case
(unfortunately, I have to type them rather than cut and paste!):

1. Direct object of a verb.
2. Indirect object.
3. Object of a preposition.
4. Subject of an infinitive.
5. Complement of the infinitive *to be* having a subject [fortunately
for the bewildered student, there's a clear example of this use and
all the others!]
6. Object of a participle.
7. Object of a gerund.
8. Appositive.

"The Elements of Style" and "The Random House Handbook" by Frederick
Crews give the same three cases. The only book in my collection that
has "the subjective or nominative case," "the objective or accusative
case, and "the possessive or genitive case" is "The Writer's Guide and
Index to English," sixth edition. (Nothing about dative, though.)

Fowler's (my Bible when I'm editing British manuscripts) lists three
pronoun cases: subjective, objective, possessive. The list is preceded
by the following passage: 

"Before the Norman Conquest, English was characterized by its use of
case-endings. Nouns, pronouns, and adjectives had a range of forms
distinguishing the nominative singular from the accusative, genitive
and dative (sing. and pl.) <snip> The main modern English prepositions
existed, but for the most part had a reinforcing rather than a
semantic role. From the Conquest onward, the case-endings rapidly
disappeared except as signs of the possessive (sing. and pl.) of nouns
and of the plural of nouns. Adjectives gradually became invariable.
Pronouns alone were left with forms that distinguish case:

"subjective   objective   possessive" <snip lists of modern pronouns
illustrating each case>

"The main casualty of this process is that because nouns form such a
dominant part of the language, and because they do not change endings
in the old accusative and dative positions, English speakers have
partially lost an instinctive power to recognize case distinctions."

(A discussion of pronoun problems follows.)

Admirably clear and concise. IMO.  

And finally, "The Cambridge History of the English Language" has this
to say:

"Personal pronouns . . . have an objective form, which nouns no longer
have. This form is chiefly used when the pronoun is the object of a
clause <snip example> and when it is governed by a preposition <snip
example>. the term objective reflects this function, and replaces the
older term accusative., favoured by traditional grammar <snip cross
reference>, *which was more appropriate for Latin.* Similarly, when a
pronoun is the subject of a clause, it is said to be in the subjective
(formerly, nominative) case" (203).

Carol, resting her case (pun intended)