Shakespeare uses soliloquies throughout act two. In scene two, Romeo speaks his most famous lines as a soliloquy - "But soft! What light through yonder window breaks?" Shakespeare uses this device to reveal his thoughts to the audience.
Friar Laurence also has a soliloquy in scene three. This time, Shakespeare uses the soliloquy to foreshadow upcoming events in the play. When Friar Laurence states, "Within the infant rind of this small flower/Poison hath residence, and medicine power," the upcoming plan to fake Juliet's death with a potion that will make others believe she is dead. Later she will awake, or at least that was the plan.
Shakespeare uses irony as well. In scene four, Mercutio makes fun of Tybalt's dueling style. This is ironic because he later dies by Tybalt's sword in a duel.
Shakes also uses allusion in scene four. Mercutio mocks Romeo's lovesick state by referring to Petrarch, who wrote love letters to a woman with the pseudonym of Laura, Dido who was abandoned by Aeneas so he could create Rome, Cleopatra, and Helen of Troy who was the spark for the Trojan War. None of these love affairs had happy endings. This again foreshadows Romeo and Juliet's fate.