Anxiety
The play is less a realistic narrative than a rendering of a single consciousness and its experience of anxiety and dread. A sense of morbid dread pervades the entire plot, as we lay in wait for ruin to befall the characters. The Old Man tries to ruin the Colonel, but gets ruined himself. The Girl dies in a fit of dread as she realizes that she is confined to a deadening life in her family home. Each of the characters must contend with the experience of dread, which turns the play into a broader meditation on the nature of dread and anxiety.
Life is Horrible
In addition to being a play about anxiety and dread, The Ghost Sonata examines the ways that life is an uphill battle, filled with struggle and sorrow. This is perhaps most succinctly encapsulated in the lines delivered by the Student at the end of the play. As the Girl begins to die, the Student delivers a monologue bemoaning the fate of man: "Where is beauty to be found? In nature, and in my own mind, when it is in its Sunday clothes. Where are honor and faith? In fairy-tales and children's fancies. Where is anything that fulfills its promise? In my imagination." This is a rather depressing and pessimistic view of the world, and depicts a life in which happiness is just an illusion.
The Rot Beneath the Façade
Everything looks like a glorious paradise to the Student upon first entering the Colonel's house, suggesting that it has always been a dream to actually get inside after passing by the house and admiring it from afar. He is also eager to meet the beautiful young woman in the Hyacinth Room and is convinced that in the Old Man he has discovered the key to achieving success. The façade is almost too perfect and serves eventually to intensify, by contrast, the rotten foundation lying beneath its veneer. In fact, the house hides many imperfections, such as the Mummy in the closet and the disobedient and vampiric servants. Even though life may appear beautiful, it is actually horrific once peels away the veneer.
Class Antagonism
The play examines the ways that class difference manifests. The Student is a poor man, and as a result wants very badly to marry the Girl, but this is impossible because she is wealthy. Additionally, we learn that certain characters that appear wealthy, such as the Old Man, were once servants, who clawed their way up to the upper echelons of society by becoming a usurer, giving out exorbitant loans to people and then bankrupting them. We also learn that the servants who work at the Colonel's home are completely ineffective and will neither do their jobs nor leave the house, which creates more trouble for the masters of the house. The Girl refers to the Hyacinth Room as the "room of ordeals," because there is always something going wrong there, often caused by a servant. In this plot point, we see a theatricalization of class antagonism, in which the servants resent their masters so much that they create work for them, and the masters have no idea how to control their charges.
The Ghost World
The play is, after all, called The Ghost Sonata, a reference to the merging between the world of the living and the dead. The Student, having been born on a Sunday, has the special ability to see ghosts. The primary ghost that he sees throughout the play is the Milkmaid, a phantom who intimidates the Old Man for reasons unknown. In addition to this actual ghost character, there are many ghostly presences in the play, and it is left unclear what exists in the world of the living and what is in the world of the dead. For instance, the Mummy is a mummified version of the Colonel's wife, the shell of a woman who has been cloistered away in a closet for years and years. The Colonel hosts "ghost suppers" at his home, at which no one speaks, which creates a ghostly atmosphere. Even though death is definitive in the course of the play, it remains unclear if it is ever actually final, or if the world of the undead is always superimposed on the world of the living.
Revenge
The Old Man's chief desire is to enact revenge on the people he imagines have wronged him. He infiltrates the Colonel's house so that he may expose the Colonel as a fraud, abscond with his mummified wife, and extort the Colonel's wealth. In the course of his revenge narrative, however, it becomes clear that he is the real villain, having been a usurer for much of his life. With the help of the servant Bengtsson, the Mummy reveals that the Old Man was once a servant who took the nourishment from his master's food like a vampire. As a result, the Mummy and the Colonel get their own revenge on the Old Man, causing him to die.
Vampirism
The Old Man, Mr. Hummel, is revealed to be a vampiric and parasitic character. His status as a money-lender, who often lends out huge sums only to bankrupt his clients, is its own kind of vampirism, a process by which he extorts resources from the people he purports to be helping. We also learn that years ago, when he was a servant at the home of Bengtsson, he sucked the nourishment out of food, handing over meals to his master which were meager and nutrition-less. The cook at the Colonel's house, a relative of the Old Man, does the same thing, remorselessly extracting the nutritional value from food, so that her employers slowly waste away. The play examines the ways that human beings feed off one another, literally or financially, and cause one another's downfall.
