Irony is used by her as a method to maintain the thematic balance of the novel Sense and Sensibility. The first irony is that Marianne intensely longed to get Willoughby as her life-friend. Willoughby was her dream boy. She dreamed to get him in her life. She had a passionate desire to live her whole life with Willoughby. But it is ironical that the situation and circumstance forced her to live her whole life with Colonel Brandon. There exists an irony, Marianne continually detested and rejected Colonel Brandon as an old man when he was paying loveless courtship to her. At that time she was having an affair with Willoughby. Brandon persistently proposed her. She persistently rejected him, calling him as a man unworthy of her. But finally the situation so forced Marianne that she had to accept him as a life-friend whom she had persistently rejected since a long time.
John Dashwood's wife left no stone unturned in trying to prevent Edward Ferrars from Elinor. But he happened to marry that woman from whom he had been prevented since a long time. There also lies the irony. There is universal irony in, the novel Sense and Sensibility. We want to live our whole life with a man/woman whom we love. But situation forces us in such a way that we have to live with somebody else. It is often said that marriages are made in heaven. Life is full of contradiction and paradoxes. Life hardly offers that which we expect it to offer. John Dashwood was a brother to Elinor and Marianne. But he was a nominal brother only. He failed to do what a brother is expected to do to sisters. Rather Sir John Middleton and Lady Middleton happened to behave to Dashwood sisters in a brotherly and filial love. A man who is a brother by relation and birth can't behave like a brother. But a man (John Middleton) is not a brother to Dashwood sister by birth, but behaves like a real brother. He provided a Barton Cottage to them. He was friendly and brotherly to them.
At the very outset, Jane Austen gives us an ironic account of the devices which Mrs. Fanny Dashwood employs in order to deprive her mother-in-law and the latter's three daughters of whatever monetary help her husband John Dashwood wanted to render to them. When John Dashwood tells his wife that he would give three thousand pounds to his stepmother, Fanny Dashwood does not approve of his intention at all; and here Jane Austen ironically says that to take three thousand pounds from the fortune of their dear little boy Harry would be impoverishing him to the most dreadful degree. And so Fanny begs her husband to reconsider his intention. She asks him how he would justify his action in robbing his child Harry, who is his only child, of so large a sum; and she further asks what possible claim his sisters can have on him when they are related to him only by half-blood. She then goes on to say that everybody knows that no affection is supposed to exist between the children of any man by different marriages. He should not ruin himself, and their poor little Harry, by wanting to give away all his money to his half-sisters, says Fanny Dashwood to her husband John Dashwood. This ironic account continues till Fanny is able to convince her husband that no monetary help need be given at all to his stepmother and his step-sisters. All that he should do for them, she says, is to send them presents of fish and game whenever these are in season. At the end John Dashwood decides that it is really not necessary for him to do anything more for his step-mother and stepsisters than such neighborly acts as have been proposed by his wife. John is satirized for intending one thing and deciding other.
One of the most conspicuous examples of irony occurs in the situation in which Mrs. Jennings thinks that Colonel Brandon is proposing marriage to Elinor when actually he is telling Elinor that he has decided to offer the Delaford living to Edward Ferrars. This is one of the most amusing situations in the novel. Mrs. Jennings has overheard only a few concluding words of the conversation between Colonel Brandon and Elinor; and those few words are completely misunderstood by her. After Colonel Brandon has left, Mrs. Jennings congratulates Elinor on what that gentleman had been saying to her. Now Elinor wrongly thinks that Mrs. Jennings has congratulated her on Colonel Brandon's generous offer of the Delaford living to Edward through her. Thus, there is a double misunderstanding here. The reader, of course, knows the real situation: and the irony here arises from the contrast between the reality as known to the reader and the wrong notions of it which both Mrs. Jennings and Elinor have formed. Subsequently, when the misunderstanding is cleared, both the ladies enjoy a hearty laugh, as we too do.
A lot of irony is to be found in the portrayals of the Steele sisters. Both sisters have a natural aptitude for flattery; and they demonstrate this aptitude fully in their relations with Lady Middleton, whose children, though very mischievous, naughty, and troublesome, are admired by the Steele sisters for being the nicest children in the world. Lucy Steele shows this aptitude for flattery later in her relations with Mrs. Ferrars too. Indeed, she is such an adept in this art that even a harsh and stern lady like Mrs. Ferrars softens towards her in view of Lucy's flatteries.
There is a lot of irony in the way in which the relationship between the two brothers. Edward and Robert, has been depicted, in the way in which the relationship between Mrs. Ferrars and her two sons has been depicted, and in the way the relationship, which develops between Robert and Lucy, is depicted. Mrs. Ferrars's treatment of her two sons, and her over-indulgence towards Robert and her quick forgiveness of Lucy have ironically been described by the author, and the other two relationships have also been dealt with in the same way. In the closing stages of the novel, we are told that, at one point, after John Dashwood has left the room, Elinor is left alone with Robert Ferrars "to improve her acquaintance with that young man"; and here we are also told of Robert's gay unconcern, and his happy self-complacency of manner while enjoying an unfair division of his mother's love and generosity, to the prejudice of his banished brother. We are also here told that Robert had earned his mother's favor through his dissipated course of life, and at the cost of his brother's integrity. There is an obvious irony in the manner in which the traits of Robert's character have been specified here because these are not "qualities" but "defects" mentioned as if they were virtues.
Perhaps the greatest irony in the whole, the novel is to be found in Robert's marriage to Lucy Steele. Mrs. Ferrars has strongly been opposed to receiving Lucy as a daughter-in-law. Robert, because of his concern about his family prestige, has been pleading with Lucy to withdraw her claim to marry Edward. Robert has held a number of meetings with Lucy in order to urge her to give up her long standing claim to marry Edward; and she has been giving Robert the impression that she would try to accede to his request. But actually Lucy has been talking to Robert in such a cunning manner that at the end Robert finds himself trapped by her as her would-be husband. And our mirth at this turn of events reaches its height when we learn that the two have got married without the knowledge of Mrs. Ferrars, and that they had eloped in order to get married. The irony here arises from the glaring contrast between what was expected by everybody, and even by us, and what actually happens.