Shakespeare rarely used the three unities, but he uses them in this play, something he has only done in one other play, The Comedy of Errors. All the events occur on the island and within one brief three-hour period. Shakespeare needed the three unities, especially that of time, to counter the incredulity of the magic and to add coherence to the plot.
The Tempest, although it is one of Shakespeare's shortest plays, still maintains the integrity of the five-act structure. In fact, most Elizabethan theatre adheres to the five-act structure, which corresponds to divisions in the action. The first act is the Exposition, in which the playwright sets forth the problem and introduces the main characters. In The Tempest, the first act establishes the nature of Antonio's betrayal of Prospero, and it explains how Prospero and Miranda came to live on the island. This first act also opens with a violent storm, which establishes the extent of Prospero's power. Most of the play's remaining characters also make an appearance in this act.
The second act is the Complication, in which the entanglement or conflict is developed. In The Tempest, the conspiracy to murder Alonso is developed, which establishes that Antonio is still an unsavory character. In addition, the audience learns more about Caliban, and Stefano and Trinculo appear, allowing the groundwork for a second conspiracy to be formed.
