Juxtaposition occurs when two things are placed side by side to highlight differences. The word comes from Latin "juxta" meaning "next" and French "poser" meaning "to place". It can involve ideas, images, characters, and actions
Juxtaposition is placing contrasting elements together to highlight their differences. Writers use it to enhance mood and themes in stories. It can create vivid comparisons between characters, settings, or ideas
A foil is a character contrasting with another to highlight protagonist's qualities. Term comes from backing gems with foil to make them shine. Shakespeare directly references foil in Henry IV, Part 1