 Harry Potter and Draco Malfoy, Sherlock Holmes and Dr. Watson, Luke Skywalker and Han Solo, Dr. Frankenstein and his creature. In each of these pairings, one character acts as a foil to the other. A foil is any aspect of a work of literature that helps us understand another aspect by providing a contrast. We get to know Harry more deeply because we see him in contrast to Draco, because Draco is calculating and selfish and mean. Harry's good intentions, generosity and bravery shine more brightly. This use of the word foil probably comes from jewelry making when a jeweler could use a foil setting to make a fake gemstone shine more brightly. This works because the foil reflects one thing, a character, an event, or a social issue back to another to help us see it more brightly. For example, in Arthur Conan Doyle's The Sign of Four, Sherlock Holmes says to Dr. Watson, observation shows me that you've been to the Wigmore Street Post Office this morning, but deduction lets me know that when there you dispatched a telegram. Right, said Watson, right on both points, but I confess that I don't see how you arrived at it. It was a sudden impulse upon my part and I have mentioned it to no one. Sherlock Holmes then explains how he figured out where Watson was, a bit of reddish mud on his shoe, a bundle of postcards on his desk, and there you have it. Watson, as always, is impressed by Holmes' power of observation and deduction. He can never tell in advance how Holmes arrives at his conclusions. And many Sherlock Holmes stories start with this kind of scene. It highlights the contrast between them, solid dependable Watson, brilliant unpredictable Holmes. What makes Watson the foil is that ultimately we learn about Sherlock Holmes more than we ever know about Watson. Holmes is the star of the show. In the conversation we just saw, for instance, Watson continues to express doubt and amazement while Holmes explains in great detail how he knows where Watson went. Watson's mind is like a blank screen for Holmes' insights, or like that bit of foil that makes the jewel of Holmes' mind shine more brightly. Foils do not only explain characters, though. They can also comment on social issues such as race or gender. In Nello Larson's 1929 novel Passing, the main characters, Irene Redfield and Claire Kendry, are both identified as black but are both able to pass as white in their segregated society. Claire, who's described as exquisite, golden, fragrant, flaunting, is passionate and desperate for social mobility. She has also passed as white for her whole adult life. Irene, her childhood friend, is firmly ensconced in the black community of Harlem. Irene feels dowdy and commonplace next to Claire, but she also resents Claire for moving back and forth across the color line as Claire pretends to be white in the rest of her life, but then visits Irene and Harlem. Claire, on the other hand, desires the life that Irene has connected to the vibrant black art scene of the Harlem Renaissance. As Irene and Claire reflect back on each other, we understand their characters better, and together they also illuminate how the black-white binary works. Harlem depends on a clear binary, a clear separation between black and white, but because both Irene and Claire can pass as white, they show how that line is actually blurry and unstable. There are no definitive physical features that can be counted on to determine race. Claire's white husband is an outspoken racist who has been unknowingly married to a black woman for over a decade. By breaking down the binary between black and white, the novel shows how race and social class always work together, since race alone isn't always clear enough to maintain separation. This is where the foil comes in again. Irene is jealous of Claire's beauty and especially her expensive clothes, which she has been able to buy only because she passes as white. In this way, Claire reflects back to Irene how desirable whiteness is made out to be. But Irene also thinks Claire is too flashy to try hard. Claire's never satisfied with what she has. In this way, Claire reflects back the price of passing as white, the hollowness of denying her past and the possibility of being part of the black community. So by seeing each character illuminated by the other, we get a more complex understanding of how race and class work together to uphold institutions like racism and white supremacy.