A poem that ridicules human folly or vice with the purpose of bringing about reform or of keeping others from falling into similar folly or vice.
The idea that morality is the basic motivation of the satirist has a good deal to be said for it, and a good deal has been said for it, often by satirists themselves and sometimes after quoting Mark Twain's remark: "Humor must not professedly teach, and it must not professedly preach, but it must do both if it would live forever. By forever, I mean thirty years. . . . I have always preached. That is the reason that I have lasted thirty years." Twain, who spent his life denouncing conventions.

Ask you what Provocation I have had?
The strong Antipathy of Good to Bad.
When Truth or Virtue an Affront endures,
The Affront is mine, my Friend, and should be yours . . .
O sacred Weapon! Left for Truth's defense,
Sole dread of Folly, Vice, and Insolence !

—Alexander Pope