In the books of The Lord of the Rings, unlike the movies, Aragorn never seems to doubt that he will eventually claim the throne, and Elrond never seems to doubt it either. I got the impression that Elrond always saw Aragorn as being different from all the heirs of Isildur who had gone before him, and many other characters seem to share this opinion.
Aragorn's grandmother predicted that he would wear a bright green stone on his breast. Gandalf had brought such a stone, called Elessar or Elfstone, from Valinor and given it to Galadriel, saying that she would one day give it to another, who would be a renewer and healer, and who would come to be known as Elessar himself (as we know, Galadriel gave the stone to Aragorn, and his royal name was Elessar). When Aragorn was brought to Rivendell to be raised by Elrond, Elrond named him Estel, which means "hope".
Later, Elrond revealed to Aragorn his true name and ancestry, and gave him the Shards of Narsil and the Ring of Barahir. We are told that the heirlooms of the Chieftains of the Dunedain, including the Shards of Narsil and the Ring of Barahir, were kept in Rivendell for safekeeping for 1,000 years, and were apparently never given to anyone before Aragorn after they came to reside at Rivendell. Aragorn falls in love with Arwen, and Elrond gives them his blessing, but says that they can't get married until Aragorn becomes king of Gondor and Arnor.
Later still, when Aragorn sets out from Rivendell with the Fellowship, Elrond orders his smiths to reforge the Shards of Narsil for the first time since it was broken 3,000 years earlier (Tolkien Gateway says: "In the books, he actually wears the broken blade and shows it to the Hobbits when they meet at The Prancing Pony in Bree, and its reforging prior to the departure of the Fellowship is a decisive move toward kingship", and since Elrond asked his smiths to reforge it, we can assume that he supported this 'decisive move toward kingship'). Arwen sets to work on making the Standard which Aragorn will bear in battle. Elrond summons the other Rangers of the North, tells them to bring the Standard to Aragorn, and asks them to remind him to seek the Oathbreakers and force them to fulfill their oath to Isildur. He sends them out to find Aragorn, and orders his two sons to go with them.
Bid Aragorn remember the words of the seer, and the Paths of the Dead.
- Elrond, The Lord of the Rings, The Return of the King, Book V, Chapter 2: "The Passing of the Grey Company"
All of this gives me the impression that Elrond was completely supportive of Aragorn, and always wanted and expected him to become king - it seems like Elrond, and many others, including Arwen and Gandalf, saw Aragorn as being different from all the heirs of Isildur who had gone before him. But some people here feel otherwise. They think Elrond opposed the marriage, didn't think much of Aragorn, and said he could only marry Arwen if after becoming king because he didn't think Aragorn could do it.
What does Tolkien say about this? Did Elrond realize that Aragorn was different from his predecessors, and would become king? Did he support Aragorn on his road to the throne? Or did he underestimate Aragorn and think that his "No marriage unless you're a king" rule would prevent Aragorn from marrying Arwen?