Antithesis
Placing two opposing ideas side by side in the same sentence or passage so each reinforces the other.
Antithesis opposes two ideas, images or words in a symmetrical structure: shadow and light, grandeur and misery, "I live, I die." Unlike the oxymoron, which welds opposites into a single expression, antithesis keeps them face to face — it is a figure of construction as much as of meaning.
It structures sentences, but also scenes, chapters, entire characters: the antithetical pair (Don Quixote and Sancho, Valjean and Javert) is one of fiction's oldest engines. Contrast makes each pole more visible — light is never seen better than at the edge of shadow.
Example
"It was the best of times, it was the worst of times"