Relationships
The central theme in this play has to do with human relationships. The dynamics of the entire play are guided by the relationships between the different characters within the play, and these relationships are a significant factor in the plot, as the characters try to discover just exactly why they feel how they do about one another. More specifically, the relationship most thoroughly discussed is marriage, as Lavinia and Edward seek to figure out just why their marriage is so difficult. With the help of Reilly, Lavinia and Edward discuss just what emotional and psychological factors go into a marital relationship, and discover that the reason they are both so drawn to and repelled by one another is the fact that they fulfill one another's most basic fears. Lavinia worries that she is unlovable, while Edward worries that he is incapable of love.
Additionally, we see other relationships, such as the relationship between Edward and his mistress, Celia, between Reilly and a number of the different characters, and between the characters as a group as they make up the eponymous "cocktail party."
Struggle
A potent theme in this play is struggle. Nothing seems to be achieved without fighting for it. Edward and Lavinia decide that the struggle to preserve their marriage is worth it and they work towards it. Reilly speaks about the existential decision everyone must make in their lives, between following the easier route of going along with society's expectations or following one's true path, which is necessarily a struggle. Celia chooses the latter, and goes to the English colonies as a missionary and nurse, where she dies a tragic death. Eliot presents a world in which everything is a struggle, but some struggles are not as bad as others.
Acceptance
In order for Edward and Lavinia to move forward in their marriage and reach some kind of peace, they must accept each other for who they are and let go of their unrealistic expectations. Additionally, they must accept the fact that they were drawn to one another because of their psychological fears, and learn to embrace the fact that they are actually quite compatible, because they mirror one another. After visiting Reilly, Lavinia and Edward make the choice to try and reconcile their relationship and find a new dynamic, one that is based around acceptance of themselves and one another. The third act, which takes place two years later, shows the couple as having moved through their struggle and accepted one another more amicably and reasonably.
Philosophy and Existence
The play's narrative is less plot-driven than it is driven by questions of existentialism and philosophy. The major conflict is the failing marriage of Lavinia and Edward, as well as the crisis of identity that Celia is suffering from. Each of these characters has developed the sense that they are at a crossroads, struggling to figure out how to live meaningful and important lives. Edward and Lavinia wonder whether their marriage is worth salvaging or whether they would be better off alone. In the logic of the play, this is as much a philosophical question as it is a romantic one, as they seek to figure out whether human beings are meant to live less meaningful lives with one another, or pursue the more difficult but spiritual rewarding path of going it alone. Celia chooses to go it alone, suffering greatly, but having suffered for a cause.
Martyrdom
In the third act, we learn that Celia has been killed by indigenous people in a fictional eastern island where she was doing missionary and nurse work. She is a white woman in the colonies, who suffers at the hands of the people she is trying to help. By suggesting that Celia's work was noble, Eliot makes her death meaningful, if horrifying, a case study of the hard road traveled by those who choose to live a more spiritually elevated life. Thus, she becomes a Christian martyr, a saintly and selfless figure who dies for her beliefs, a Westerner who lives selflessly and dies for her desire to help non-Western people. Racist and colonial though this theme may be, it is a central part of the play's logic and its depiction of England.
Public versus Private
The play centers around the scenario of the "cocktail party," a social endeavor in which people seek to check in with their social set without going terribly deep. The scene opens on a cocktail party of wealthy Londoners recounting stories they have already told one another in a glib and bored tone. Then, even after they all leave, and Edward is left alone, the individual guests keep popping in and meddling in his affairs. He cannot seem to get a moment of privacy, which is all he wants.
Then, when Edward and Lavinia talk about what has been so difficult about their marriage, they discuss the fact that Lavinia was always wanting Edward to be the kind of husband who could prop up her public life as hostess. They represent the two ends of this spectrum, Lavinia the public and Edward the private. By the end of the play, they have reconciled this difference, and become successful hosts together, looking forward to the moment they can escape to their country home.
Love
As a theme, love emerge when Lavinia and Edward make an effort to save their dying marriage. Lavinia insists that her greatest fear is that she is unlovable, while Edward says that he has always worried that he was incapable of love. It is this strange equation, Reilly suggests, that has drawn them together, and which makes up the substance of their marriage. Love is rarely spoken about as an available emotion in the play, but rather as something that is running scarce. The substance of Edward and Lavinia's marriage has less to do with love than it does with a mutually advantageous dynamic and social contract.
