Austen uses irony as a means of moral and social satire. Her sentences, while usually simple and direct, contain within them the basic contradictions which reveal profound insights into character and theme. This is most obvious in her blunt character sketches. John Dashwood "was not an ill-disposed young man, unless to be rather coldhearted, and rather selfish, is to be ill-disposed." Note that in the first half of the sentence, she seems to be viewing his character amiably. Suddenly she changes direction, and the general impression we receive about John is far more bitingly negative than a mere statement of disapproval. Thus she contains in her statement all the elements of disapproval without directly stating that he was ill-disposed.
Her irony ranges from the gentle to the severe. When she speaks about Marianne, she says, "She was generous, amiable, interesting: she was everything but prudent." Austen weights the first half with pleasing commentary and gently undercuts it in the second. Compare this with her biting description of Mrs. Ferrars: "She was not a woman of many words; for, unlike people in general, she proportioned them to the number of her ideas." Austen begins innocently enough, but the conclusion of that sentence bitterly reveals to us the impression she wishes us to have. Reflection is necessary, for we must see the sentence as a whole. She seems to be contradicting herself, but this is not so. We had just taken it for granted that she would finish the sentence the way we expected it to be finished. Our expectations built in the first part of the sentence are disappointed. But the change in tone, though seemingly sudden, is a natural conclusion to the author's own train of thought. She knew that Mrs. Ferrars had nothing to say, but in the order, meticulously constructed, in which she reveals this information, lies her genius. The necessary reflection, subsequent surprise, and devastating insight create an effect which is much more persuasive than direct statement could be.