How Does The Title, “A Modest Proposal,” Tell The Reader That The Piece Is Satirical?

The author is pretending to be very serious and proposing that people eat babies—something that would never happen in reality. He's being sarcastic and making fun of people who make proposals like these. In addition, he's also mocking people who are so poor that they have to eat babies. So by using this title, he is able to convey his message without having to say anything directly about what he thinks about these things himself; all he has to do is write about them as if they were real proposals for real problems and let the reader draw their own conclusions about what's going on here!

The proposal itself—to eat babies—is so absurd that it seems like a joke. And Jonathan Swift's tone is so serious, that he might as well be proposing a real solution to Ireland's problems. But then there's the subtitle: "For Preventing the Children of Poor People in Ireland, From Being a Burthen to Their Parents or Country, and For Making Them Beneficial to the Publick." This subtitle contains two key elements: first, it makes clear that this is not just a joke—it's actually meant to be taken seriously; and second, it names the satire by making clear what kind of "proposal" this is—a "modest" one.

The piece is in fact anything but modest—it contains a call for cannibalism and a suggestion that children be eaten by their parents. The title suggests that this will be a serious proposal, with no hint of satire or humor. But when you read the piece itself, you realize that it's actually mocking the idea of a serious proposal.