Antithesis is a literary device in which two opposing ideas are expressed within close proximity. One good example of antithesis can be seen in Alexander Pope's famous line, "To err is human, to forgive, divine." Dr. Wheeler also uses as an example of antithesis in his definition, "I burn and I freeze" (Wheeler, "Literary Terms and Definitions").
One antithesis in A Midsummer Night's Dream can be found in the opening scene. Hermia uses antithesis in reply to the Duke who is trying to make her to submit to her father's will. When Duke Theseus reminds Hermia that she must learn to view things using her father's "judgement," Hermia begs her pardon, saying, "I know not by what power I am made bold, / Nor how it may concern my modesty" (I.i.61-62). To be bold, means to be brave, fearless, and even "flashy," and "showy" (Random House Dictionary). On the other hand, the word modesty refers to being moderate, simple, and humble, which is the exact opposite of being bold (Random House Dictionary). Since boldness and modesty are complete opposites, or antithetical, we see that this is a perfect example of antithesis.