Satire is a literary form that uses the literary device figure of speech called irony. In other words, irony is a tool available, along with ridicule, sarcasm (a form of irony), wit, scorn and exaggeration, within the literary form of satire. Jane Austen is noted for saying in her letters that she laughs at people and herself in her novels. It is precisely this "laughing at" that comprises the literary form of satire. Irony, a device of satire, is a sophisticated understanding of the difference between what is and what ought to be; an understanding that what is is different from what is expected to be.
Satire laughs at humanity to reveal human weakness; to point out hypocrisy; to reinforce a widely spread and accepted moral or value code. The aim is to prompt individuals to return to a truer, more sincere and genuine following of the code. Satire succeeds when the readers laugh along with the author.
In the opening lines of Chapter 1 of Pride and Prejudice, Jane Austen makes it abundantly clear satire will be one hallmark of the novel. She opens with the outrageous statements:
It is a truth universally acknowledged, that a single man in possession of a good fortune must be in want of a wife.
However little known the feelings or views of such a man may be on his first entering a neighborhood, this truth is so well fixed in the minds of the surrounding families, that he is considered as the rightful property of some one or other of their daughters.
This quotation uses exaggeration ("universally acknowledged"), ridicule ("However little known the feeling or views of such a man"), and irony ("he is considered as the rightful property of...their daughters") to laugh at husband-hungry women who presume on men's cooperation without ever having become even slightly acquainted with them.
The initial conversation between Mr. and Mrs. Bennet is replete with irony (e.g., the exchange about "design") and is itself satirical. Indeed, Austen's description of Mr. Bennet is a fair definition of satire: "quick parts, sarcastic humor, reserve, and caprice." Throughout, Mrs. Bennet is being earnest in her conversation and Mr. Bennet is mocking and silently laughing at her, although she only laughs with him after she finds out that he make the visit to Mr. Bingley that he initially refused to make.