Mercutio, the witty skeptic, is a foil for Romeo, the young Petrarchan lover. Mercutio mocks Romeo's vision of love and the poetic devices he uses to express his emotions:
Romeo, Humors! Madman! Passion! Lover!
Appear thou in the likeness of a sigh,
Speak but one rhyme and I am satisfied.
Mercutio is an anti-romantic character who, like Juliet's Nurse, regards love as an exclusively physical pursuit. He advocates an adversarial concept of love that contrasts sharply with Romeo's idealized notion of romantic union. In Act I, Scene 4, when Romeo describes his love for Rosaline using the image of love as a rose with thorns, Mercutio mocks this conventional device by punning bawdily:
If love be rough with you, be rough with love;
Prick love for pricking and you beat love down.
The Queen Mab speech in Act I, Scene 4, displays Mercutio's eloquence and vivid imagination, while illustrating his cynical side. Mercutio, unlike Romeo, doesn't believe that dreams can act as portents. Fairies predominate in the dream world Mercutio presents, and dreams are merely the result of the anxieties and desires of those who sleep.
Mercutio's speech, while building tension for Romeo's first meeting with Juliet at the Capulet ball, indicates that although Mercutio is Romeo's friend, he can never be his confidant. As the play progresses, Mercutio remains unaware of Romeo's love and subsequent marriage to Juliet.
When Mercutio hears of Tybalt's challenge to Romeo, he is amused because he regards Romeo as a lover whose experience of conflict is limited to the world of love. So he scornfully asks: "And is he such a man to encounter Tybalt?" (II.3.16-17). Mercutio seems to exist outside the two dominant spheres of Verona because he takes neither the world of love nor the feud seriously. However, Mercutio, like Tybalt, is quick-tempered and they are both ready to draw their swords at the slightest provocation.
Mercutio is antagonistic toward Tybalt by suggesting that Tybalt is a follower of the new trends in swordsmanship, which he regards as effeminate. Like Tybalt, Mercutio has a strong sense of honor and can't understand Romeo's refusal to fight Tybalt, calling it, "O calm, dishonorable, vile submission" (III.1.72). Mercutio demonstrates his loyalty and courage when he takes up Tybalt's challenge to defend his friend's name.
The humor with which Mercutio describes his fatal wound confirms his appeal as a comic character: "No 'tis not so deep as a well, nor so wide as a church door, but 'tis enough, 'twill serve" (III.1.94 — 95). Mercutio's death creates sympathy for Romeo's enraged, emotional reaction in avenging his friend's death. His death marks a distinct turning point in the play as tragedy begins to overwhelm comedy, and the fates of the protagonists darken.