Themes are the fundamental and often universal ideas explored in a literary work.

Speech as Mode of Action

David Mamet is famous for his attention to detail in dialogue. All the characters in Glengarry Glen Ross have very specific speech patterns. Words are often left out of sentences, and the grammar, though rarely "proper," always makes intuitive sense. For example, Mamet will have a character say "should of" instead of the grammatically correct "should have," because, first and foremost, Mamet is trying to reflect the way he believes his characters would actually talk. Moreover, Mamet believes that the way people speak influences the way they behave, rather than vice versa. Every comma, every stutter, every emphasis—note that single syllables are often placed in italics—in the play is as Mamet expects it to be performed. The stage directions, however, are so sparse as to be nearly nonexistent. Mamet does not specify how the set looks and almost never specifies what the characters' physical actions may be. Furthermore, at times in Act Two, with characters coming in and out of Williamson's office, Mamet is even ambiguous about who is or is not onstage at certain moments. These physical details are irrelevant to the drama that Mamet is creating, which is all in the talking.

Characters' ability to speak persuasively determines their fate in Mamet's world. Roma is a breathtakingly smooth talker, able to come up with lies and philosophies as quickly as the words can leave his mouth. His continued business success is never in doubt. Levene, on the other hand, is a disastrously poor persuader. We see from his first line—in which he stammers out seven words and pauses before he can even begin his sentence—that he is not well suited to sales. Levene makes desperate pleas throughout the play, yet nearly every argument he makes seems to make things worse for him. Moss and Aaronow, the other two salesmen in the play, fall somewhere in the middle: Moss does not have anything approaching Roma's suavity, but he does have a brute aggression with his words that could conceivably overpower a customer; Aaronow, though meek, at least does not exude desperation the way that Levene does.

Success and Failure

Glengarry Glen Ross is a scathing attack on American business practices. The only characters in the play whom we do not witness in some attempt to steal from, cheat, or trick one of the others are Aaronow and Lingk—both extremely meek men who, it is implied, do not have much chance at great success. The sales office of the play serves as a microcosm of capitalist culture: as the top man gets a Cadillac and the bottom man gets fired, every man must not only work for his own success but also hope for—or actively engineer—his coworkers' failure.

The top salesman on the board—at this point, Roma—is also entitled to the best leads. Success, then, is rewarded with further opportunity for success, while failure is punished with the guarantee of further failure. The system is brutal and compassionless. Levene grasps at anything that might help him appear successful, but his guise is unfortunately transparent, which only makes him appear like a greater failure. Like a man flailing in quicksand, Levene's struggle to evade failure at all costs ends up hastening his professional demise. At the play's climax, Levene asks Williamson why Williamson is going to report him to the police, and Williamson responds, "Because I don't like you." This response is borne partly of Levene's having recently insulted Williamson, but it is also because Levene has been emitting an air of failure from the start of the play, and Williamson, a businessman himself, has been trained to fear and hate failure.