: : Aragorn was basically claiming the throne as Elendil's Heir,
: : not as either Isildur's (a claim which had been rejected) or
: : Anarion's (which claim, apparently, he could not assert
: : because Gondor recognized only candidates descended of a male
: : line).

: There's no question that he was, ultimately, claiming the High
: Kingship; as a direct male lineal descendant of Elendil, he had
: the right. And as things worked out, he did in fact reign as
: the High King -- and only King.

: I'm not sure I agree with the rest of what you say here,
: however. Even before his crowning, he was hailed as the "King
: of Gondor," not some other formula, such as the King of the
: West (as he is referred to at the final breaking of the
: Fellowship at Orthanc), or High King of the Numenoreans, etc.

Aragorn is referred to as "The King of Gondor and Lord of the Western Lands" by Gandalf in "The Field of Cormallen". He assumed the throne with greater authority than any king before him (including Isildur, who became King of Gondor years before he became King of Arnor).

: In regards to his claim on the throne of Gondor (as opposed to
: the High Kingship), he did indeed have a claim, particularly
: seeing as he was the _only_ lineal male descendent of Elendil
: remaining.

It is by no means clear that Aragorn was the only lineal male descendant of Elendil left. He had kinsfolk in Eriador (including Halbarad, though he died) who were descended of the Line of Isildur. His grandfathers were both descendants of Aranarth, for instance.

: It is true that Pelendur, the Steward of Gondor, rejected the
: claim of Arvedui, to Gondor's crown following the
: death of Ondoher and his sons in 1944 T.A, arguing that the
: succession was reckoned only by male descendents (rejecting
: Arvedui's marriage to Ondoher's daughter as a claim), and that
: it was reserved exclusively for the Line of Anarion. This does
: not appear to have been an irrevocable law (as evidenced by the
: fact that it did not keep Faramir from recognizing Aragorn's
: claim), nor a particularly well-founded decision, as Arnor's
: response indicated in citing the example of ancient Numenor's
: royal succession by the eldest offspring regardless of sex.

Faramir did not present Aragorn's claim in the same manner as Arvedui had presented his.

  "Then Faramir stood up and spoke in a clear voice: 'Men of
  Gondor, hear now the Steward of this Realm!  Behold! one has
  come to claim the kingship again at last. Here is Aragorn son
  of Arathorn, chieftain of the Dunedain of Arnor, Captain of
  the Host of the West, bearer of the Star of the North, wielder
  of the Sword Reforged, victorious in battle, whose hands
  bring healing, the Elfstone, Elessar of the line of Valandil,
  Isildur's son, Elendil's son of Numenor.  Shall he be King
  and enter into the City and dwell there?'"

: The lack of respect that Gondor had for the Line of Isildur
: and Arthedain, and reluctance to cede control to an outsider
: -- not to mention Earnil's fresh victory laurels -- probably
: had more to do with Pelendur's decision than the Gondorian
: custom of male succession. I suspect that if Earnil had been,
: say, Ondoher's sister-son, and were the only claimant left,
: Pelendur would have happily altered the succession custom for
: him.

I know of no evidence that attests to a lack of respect in Gondor for the Line of Isildur. Certainly he was still honored as one of the founding kings of the realm. Tolkien describes Pelendur as playing the chief part in rejecting Arvedui's claim (Appendix A to LOTR).

Originally, Pelendur was to rule Gondor sixteen years before giving the throne to Earnil, but Tolkien changed that. So Pelendur's motives are suspect but unconfirmable.

: In any case, one key condition had changed between 1944 and
: 3019: the Line of Anarion was extinct -- or to the extent
: that it was alive, it had been rejoined with Isildur's line
: with Arvedui's marriage to Finduilas, and lived on in Aragorn
: himself. Either way, it seems that the crown of Gondor
: defaulted to the Line of Isildur with the absence of any
: claimants (male or otherwise) of the line of Anarion.

Had it been so simple a matter, there were many previous candidates who could have claimed the throne. In early versions of the "Tale of Years" Tolkien says they actually made the claim, but this assertion was dropped from later versions (including the final, published version).

Aragorn's situation differed from Arvedui's in many ways:

1) Aragorn was indeed a descendant of Aranarth, but Faramir
did not present this claim. Hence, the descent through
a daughter's line was still held invalid. The Stewards
themselves were ultimately of royal origin according to
Tolkien, and yet they could not claim the throne, probably
because they were descended of a daughter somewhere.

2) Aragorn proclaimed himself to be Elendil's Heir. Eomer
mentions this in "The Houses of Healing": "Already you
have raised the banner of the Kings and displayed the
tokens of Elendil's House."

3) Aragorn was wielding Elendil's sword. Even Isildur had
never done that (although he had certainly possessed the
shards).

4) Faramir was already disposed to treat Aragorn's claim
with an open mind. He did not reject it out of hand
when he discussed it with Frodo (who also referred to
Aragorn as "descended in direct lineage, father to
father, from Isildur Elendil's son himself. And the
sword that he bears was Elendil's sword.") in "The
Window on the West". And note, too, that Faramir's
men are not moved by the mention of Isildur (even in
Ithilien as Rangers of Ithilien) but rather by the
mention of Elendil's sword.

5) Aragorn's homeland was not threatened, whereas Gondor
was. In Arvedui it was the other way around. Gondor
was flush with the victories of Earnil and Arnor was
recognizably in peril of being destroyed.

The claim of Isildur was really without meaning in Gondor. It was the restoration of Elendil's House that Aragorn brought to the south, not the restoration of the Lines of Isildur or Anarion. Both had failed in one way or another, and Gondor which lived on precedent could not recognize a claim previously rejected.

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Parma Endorion: Essays On Middle-earth, Revised Edition