The Decoy Answer

The decoy answer is this site's name for the first answer to a puzzle that looks right and is shown, by checking, to be wrong. The puzzle's wording, or a reader's first instinct, sets it up.

How the decoy answer is used

In a puzzle entry with a single checkable answer, the decoy answer comes right after the puzzle itself. The entry states it openly and explains why it is tempting: which condition it quietly drops, which rule it misreads, or which step it skips. The correct answer, with the check that confirms it, sits in a fold just below, so you can try the puzzle before you open it.

Three puzzle entries use it this way. On the Tower of Hanoi page, the decoy answer is a small move count that lets each smaller disk step aside just once. In the featured knights and knaves puzzle, it is a verdict on A taken from the tone of the accusation rather than from the rules. For the river crossing puzzle, it is the claim that no safe order of crossings exists.

The decoy answer is shown first because the part of a puzzle worth learning is why the obvious route fails. Where that route breaks is something you can look for again in the next puzzle, even though its answer will be different.

A decoy answer has to fail a check, not merely look naive. The correct answer to every such puzzle is confirmed by exhaustive search or with a solver that lists every solution, and the decoy answer is named only when that check rules it out.

Where the term is never used

The decoy answer applies only to puzzles whose rules can be written down in full and whose answer can be checked. It is never used for a disputed paradox, where the answer depends on which logic or decision rule you accept. In those entries the competing positions sit next to each other in a table, each with its premises and its source, and none of them is called a decoy. Philosophers who hold a position that the site does not share are not giving a wrong answer.

The term is also not a label for a reader's guess. It names one specific wrong answer that the entry has identified and checked against the rules.

Related terms

Two other terms are defined on this site: the swap test, used in dilemmas, and the lone count, used for numbers that have no denominator. The About page explains how puzzle answers are checked.