How does the quote below from Romeo and Juliet show the contrast between hate and love?
"Here’s much to do with hate, but more with love. / Why then, O brawling love, O loving hate, / O any thing, of nothing first create."
the device Shakespeare uses to show the negative side of love is an oxymoron. By placing opposites side by side, he generates nuggets of wisdom concerning the darker side of love. In modern English we use similar idioms such as "love hurts' or "love to hate." There is a firm belief that the stronger one's love, the stronger the ability to hate,
For Romeo his dissolving feelings for Rosalind and his as yet unrequited love for Juliet create the beautiful oxymoron Shakespeare has him utter. In addition, Romeo will battle out of love, but will hate the necessity to do so.
Note that in modern times, traditional marriage vows express opposites or extremes: for better for worse, for richer for poorer, in sickness and in health. By reading on, notice Shakespeare's continued use of the oxymoron as he gives further examples of the duality of love, duality being a favored motif/theme device of Shakespeare's.