The principal themes of John Guare's Six Degrees of Separation are the connections between people and the motives that drive their behavior toward one another.

The first of these themes is evident in the title. People are connected to each other in ways that they would not have imagined. Paul gains entry to the Kittredges' home and their world by pretending to have a connection with them that does not exist. However, he remains connected to them in other ways, as Ouisa Kittredge remarks in the play's most famous monologue:

It's a profound thought. How Paul found us. How to find the man whose son he pretends to be. Or perhaps is his son, although I doubt it. How every person is a new door, opening up into other worlds. Six degrees of separation between me and everyone else on this planet. But to find the right six people.

The second theme, that of motivation, is explored first through the snobbery of the status-conscious Kittredges, who are motivated to help Paul when they believe he is the Harvard-educated son of a Hollywood star. Speculation about the motives behind Paul's destructive, sociopathic conduct also contributes to the theme, as does his most famous monologue in the play, a meditation on why The Catcher in the Rye, a "touching, beautiful, sensitive story," has motivated so much violence and hatred.