The central theme of "Persuasion" is, ofcourse, constancy in love. Although, it is eight years since the match between Anne and Wentworth has broken off, both of them did not marry someone else although there were opportunities to do so. Anne was solicited by Charles Musgrove who on being refused by her married her younger sister Mary. Wentworth came close to marrying Louisa Musgrove who after her accident at Lyme Regis fell in love with Benwick and got married to him.
This issue is debated very comprehensively by Jane Austen in Ch.23. The incident takes place in the room of the inn 'The White Hart' in Bath where the Musgroves have been lodged. They have come to buy wedding clothes for Henrietta. Captain Harville and Wentworth are also present in the same room.
Captain Harville is the brother of Fanny Harville who was expected to marry Benwick, but unfortunately she died before that. Benwick went into deep mourning and every one expected him to remain single for the rest of his life; but after Louisa Musgrove fell down and hurt herself she was looked after by Benwick. The intimacy that developed then quickly blossomed into love and Benwick decides to marry Louisa. When Benwick was in love with Fanny Harville he had a painting made of himself and gifted it to her. But now Captain Harville has been asked by Benwick to frame the same picture so that it can be presented to Louisa. Captain Harville is very depressed and disconsolate and tells Anne: "Poor Fanny, she would not have forgotten him so soon." Anne supports him and remarks, "it would not have been in the nature of any woman who truly loved."
Then both of them debate as to who is more constant in love, man or woman. Anne ofcourse strongly supports her own sex by saying, "we certainly do not forget you, as soon asyou forget us." Captain Harville quotes examples from history and literature to prove his point. Anne rejects his arguments by remarking, "men have had every advantage of us in telling their own story....The pen has been in their hands. I will not allow books to prove any thing."
Later in the course of this argument, Captain Harville says that he spoke only on behalf "of such men as have hearts!" Immediately Anne corrects herself and remarks, "I should deserve utter contempt if I dared to suppose that true attachment and constancy were known only by woman. No, I believe you capable of every thing great and good in your married lives."
Captain Wemtworth who had been listening intently to this discussion is prompted by this last remark of hers to propose to her the second time in a letter, which he manages to pass on to Anne. This time Anne has no hesitation in accepting his proposal.