What structural devices are there in Hamlet?

Shakespeare employs a number of important elements in his plays. In Hamlet, the existence of foils and the use of the soliloquy are both important devices that help develop Hamlet's character. The plot of Shakespeare's Hamlet, however, depends mostly upon two significant structural devices: the presence of the supernatural and the elective monarchy.
When the ghost makes his first appearance to the guards and then to Horatio, an eerie and foreboding mood is established. When Hamlet meets his father's ghost at the palace gates the meeting acts as the exciting force that sets the rest of the play into motion. Hamlet receives the order to avenge his father's murder. The ghost also serves a secondary function: to make Hamlet question whether or not the desire is real, and if indeed the ghost is his father or the devil assuming a pleasing shape. The use of the supernatural, then, is integral to the plot as it both gives Hamlet his purpose as well as his reason to question it.
The elective monarchy itself is another significant device. If the crown would follow the rules of primogeniture, King Hamlet's death would precipitate the rise of his son, young Prince Hamlet, to the throne. Because it is an elective monarchy in Denmark at the time and in the play, the system allows for Claudius's motive.
While there are a number of structural devices in the play, the use of the supernatural and the implementation of the elective monarchy are both interesting and impactful.