[Lalwendë]

I don't see any point where Boromir acknowledges Aragorn as rightful King of Gondor on that journey from Rivendell to Amon Hen. On the contrary, Boromir's actions and speech whenever he is with Aragorn seem quite strained and conflicting at times. They argue and Boromir is on more than one occasion silenced by Aragorn who he does accept, on the surface at least, as leader of this fellowship, but not as his King.

If Boromir is following anyone, then he is following Frodo. He makes a point of asking what the Ringbearer thinks about one choice, and there is this very revealing passage:

Boromir held out long against this choice; but when it became plain that Frodo would follow Aragorn, wherever he went, he gave in. 'It is not the way of the Men of Minas Tirith to desert their friends at need,' he said, 'and you will need my strength, if ever you are to reach the Tindrock. To the tall isle I will go, but no further. There I shall turn to my home, alone if my help has not earned the reward of any companionship.'

Here Boromir also reveals his feelings towards the rest of the fellowship. He says he is their friend and would not desert them for that reason, but then says something about how he perceives their friendship: alone if my help has not earned the reward of any companionship. He starts off speaking in a high minded tone of honour but ends on a rather sad note. Boromir seems to feel he has no real friends in this Fellowship. Does he truly have no friends? Or are his own goals very much on his mind, driving his actions and speech? That goal, at this point, is to stay with Frodo and to endeavour to persuade Frodo to come to Minas Tirith. Boromir's efforts of persuasion have been subtle, but have been growing ever stronger, mere questioning of their path has passed from moaning and into doomsaying by the time they leave the river. Of course his efforts will culminate in his desperate measures at Amon Hen, when he takes advantage of a wekness in Aragorn's leadership, his indecision.

I think Aragorn knows or at least suspects what Boromir is up to; his efforts at persuasion are growing increasingly less subtle. And I also think that this is causing the relationship between the two men to come under increasing strain.

"Farewell, Aragorn! Go to Minas Tirith and save my people! I have failed."

This is also revealing. Boromir, even in death, issues an order. He expects that now Frodo and the Ring have gone, that Aragorn ought to go right away to Minas Tirith. He also calls those people my people. Not our people, let alone, your people, but my people. He has faith in Aragorn at this point, but as King?

Tolkien of course reveals to the reader early on that Aragorn is this rightful King by blood. He also shows us Aragorn's failings and how much he has to learn on his way to the throne e.g. respect for lesser Kings. Likewise he spends most of three books gradually revealing the proofs that Aragorn needs to claim this Kingship, whether symbolic (Palantiri, healing hands etc.) or in his skills as a leader. We have the benefit of knowing Aragorn's destiny, the people he meets, however, do not. In a very real sense he earns his Kingship through merit, and that makes him a better King.