Irony is one of those things we know when we see it, but it’s hard to pin down if you’re asked to explain. Merriam-Webster gives two definitions: (1) the use of words that mean the opposite of what you really think especially in order to be funny. (2) a situation that is strange or funny because things happen in a way that seems to be the opposite of what you expected.

The first meaning of irony is often confused with sarcasm. Sarcasm always involves mockery. Some ironical statements are also sarcastic, e.g., “Brilliant!” in response to something stupid. Irony has other uses, though.

You can use irony to make light of something unpleasant or difficult: “Piece of cake!” in response to a daunting task or “Lovely weather today” when caught in a storm. You can employ it for simple humor: “Don’t forget your sunscreen” when going into a cave. Sometimes irony conveys solidarity with the listener by suggesting something which both know is absurd but the average person might not. Here’s a real-life example: “October is Computer Security Month. Change all your passwords to october123 and tell everyone, to promote the event.” That can be risky if people who aren’t in the know take your suggestion at face value.

The second definition applies to situations, not statements, so it isn’t easy to confuse with sarcasm. But when is a situation ironic and when is it just unexpected or disappointing? “Strange” isn’t quite right. If you check your car over very carefully and then it breaks down half a mile down the road, that’s unexpected and strange, but I wouldn’t call it ironic. The heart of the second kind of irony, I think, is the sense that the previous situation contained the roots of an unexpected reversal. Otherwise it’s just something going wrong. If your car breaks down because of all the work you did on it, that’s irony.

It’s ironic that Robert Schumann permanently injured his hand using a device that was supposed to strengthen it. It wouldn’t be ironic if he crippled it in an ordinary accident. If you go to great lengths to solve a problem only to realize that a simple solution had been in front of you the whole time, that’s irony. If your can’t find any solution, it isn’t. “Bad stuff happens” isn’t irony as such.

Irony of situations is an effective device in writing. In non-fiction writing, it can highlight how bad things happen in spite of a person’s intentions, or it can serve as a warning against actions that seem good but aren’t. In fiction, it can add surprise, poignancy, or humor to a frustrated course of action. In Macbeth, the witches’ prophecy is literally true, but following it leads Macbeth to destruction. In Orwell’s 1984, all of Winston Smith’s attempts to fight the authoritarian state turn out to have been tracked and even guided by Big Brother. In John Campbell’s “Who Goes There?” the hostile alien’s drive for self-preservation is its undoing.

Slapstick comedy is built out of irony. A man walks confidently down the street and slips on a banana peel. A crook’s honest sidekick tries to help the victims and ends up taking the punishment.

The Twilight Zone regularly used irony to deliver poetic justice. A nasty fellow wishes that all the “evil” people in the world would shrink to midget size, and he’s the one who experiences that fate. An immortal commits murder to show the futility of executing him, and his sentence is commuted to life imprisonment.

Irony of words can create memorable names. In The Hitchhiker’s Guide to the Galaxy, an alien on Earth names himself Ford Prefect (an automobile once sold in England) because he thinks it sounds inconspicuous. In The Magic Battery, my witch-hunting villain is named Gottesmann (“man of God”).

Irony can become nihilistic when it runs to excess. It can seem to say that all human effort is futile. But used properly, irony (in both senses) is a valuable writer’s tool.