Irony

Irony is a gap between appearance and reality — between what a speaker says and what they mean, or between what a situation promises and what it delivers — which the audience is expected to see.

Three things share the name, and conflating them is the usual source of confusion.

Verbal irony. The speaker says the opposite of what they mean, and expects to be understood. Wonderful. Another form. The tone, or the situation, tells the reader to invert the sentence. Litotes is a mild, structured form of the same move; sarcasm is verbal irony aimed at someone.

Situational irony. The outcome is the opposite of what the situation promised. The fire station burns down. The safety inspector falls down the stairs. It is a property of events rather than of language, and it is the kind most often used loosely, for anything that is merely a coincidence.

Dramatic irony. The audience knows something a character does not, so ordinary lines carry a second meaning. That one has its own entry, because it is a structural tool rather than a figure of speech.

What all three share is a reader who can see both layers. Irony that the audience cannot detect is not irony; it is an error, and this is the practical risk. Verbal irony on the page has no tone of voice to carry it, so the surrounding scene has to establish the gap first. An unreliable narrator is a whole book built on that principle.