In Act 3, Scene 2, why does Juliet use so many oxymorons?
It is actually Shakespeare who uses so many oxymorons, such as the following:
Beautiful tyrant! fiend angelical!
Dove-feather'd raven! wolvish-ravening lamb!
A damned saint, an honorable villain!
Shakespeare has Juliet doing this for several reasons. One is that it illustrates her confusion about her feelings. She loves Romeo but blames him for killing her kinsman Tybalt. She has to incorporate both feelings into her young, sheltered view of the world and of humanity. The oxymorons are also a poetic novelty in this play. They afford some amusement to Shakespeare's audience while at the same time showing Juliet's reaction to the bad news. She is just beginning to sense the possible consequences of the fatal duel. It may mean that Romeo will be executed. It could have disastrous consequences for her marriage and her newfound happiness.
Romeo's duel with Tybalt marks the turning point in the play. Juliet's reaction shows that reality is already intruding into the illusion of perfect love. This young girl is torn between her ties to her family and her new ties to her handsome and passionate young husband. The oxymorons mainly serve to illustrate her confusion and mental anguish.
At the beginning of the scene, Juliet is excitedly anticipating the arrival of her new husband, Romeo. In this moment, she is all happiness. However, after her Nurse tells her the news —that Romeo has slain Tybalt, Juliet's beloved cousin—her emotions become, suddenly, a great deal more complex. Her use of oxymora helps to communicate the increased nuance and complexity of her feelings. She calls Romeo a
Beautiful tyrant! Fiend angelical!
Dove-feathered raven, wolvish-ravening lamb!
A damned saint, an honorable villain! (2.3.76-80)
Now, instead of thinking of him merely as "Beautiful" or "angelical," she also characterizes him as the opposite: because he has proven murderous, of her family member especially, she sees him, in part, as a "Fiend" or someone who is unrestrained and brutal, a "tyrant." Juliet still thinks of Romeo as a "saint" and an "honorable" person, but in light of his actions, she cannot but temper these positives with negatives, that he is a "villain," deserving of her curses. He is her beloved husband, but now he is also the murderer of her cousin, and this fact alters the way she conceives of him.