A foil is a character who contrasts with another, usually the protagonist, so that the other character's traits, choices or flaws stand out more sharply.
Where the term comes from
Britannica defines a foil in literature as a character presented as a contrast to a second character so as to point to, or show to advantage, some aspect of the second. Its example is Dr. Watson in Arthur Conan Doyle's Sherlock Holmes stories: his relative obtuseness makes Holmes's deductions seem more brilliant. Merriam-Webster lists the same sense among the meanings of foil, someone or something that serves as a contrast to another, and illustrates it with a performer who acted as a foil for a comedian. The same dictionary entry also lists the jeweller's sense, a thin piece of material set under a stone to add colour or brilliance, which is a helpful picture for how a foil works in a story.
An example
Hesper is a cautious archivist who reads the plaque before she touches a door. Ludo is a courier who has never met a lock he did not try to kick. When the two of them reach a sealed cellar, Ludo kicks it and Hesper notices that the dust on the handle has been disturbed. Neither choice is wrong, but each makes the other look sharper: Ludo's impulsiveness makes Hesper's care look like wisdom, and her care makes his speed look like courage. Later, when Hesper finally breaks a rule, the reader feels the cost, because they know how rarely she does.
Common mistakes
- Building a foil as cardboard. The contrast works when the foil has their own wants and a point of view.
- Contrasting everything. One or two traits tied to the story's central question are enough; opposing every trait makes a caricature.
- Treating a foil and an antagonist as the same role. Watson is no enemy of Holmes, and a foil can be an ally, a rival or a friend.
- Letting the foil outshine the character they illuminate, so the story seems to be about the wrong person.
How to check your manuscript
Write a short list of your main character's most important traits. Beside each, write the character who shows it most clearly by contrast. If none does, you may have a foil missing, or a foil who does not appear in enough scenes. Then check that the contrast shows up in choices, not just description: find a scene where both characters face the same problem and answer it differently. For related roles, see protagonist and antagonist, and for building characters with their own wants, character development.
In Musael, world and characters lets you link entries by relationship, so a pair of foils stays connected in your codex.