Why do you think Sam Shepard included the Old Man in the play? How would the play be different if the Old Man came in the door and talked to Eddie, Martin and May?
The Old Man serves as a witness, observer and audience for the relationship between May and Eddie. He sees them from outside of themselves but he also represents their feelings within. He shows the theater audience that there is no right or wrong version of the story and that truth is not always fact in this play. The Old Man is not really in the motel room but in their minds. He serves as a reminder of their kinship and of the shame of their incestuous affair. The Old Man helps the theater audience know what to make of Eddie and May's torrential and competitive conversations by adding humor and irreverence to the story. By being in another place and time while also being close enough to witness the events in the motel room and to interact with May and Eddie the Old Man emphasizes the dream-like quality of the play and the non-realistic tone it takes. The play is a heightened reality a landscape of the high and low emotions of the subconscious and the Old Man's presence contributes to that setting.
If the character of the Old Man came in the door rather than staying in his own world, he would have a realistic conversation with May and Eddie. They might talk to him or shun him. They might reveal their feelings to him about each other. They might disrespect him for treating their mothers so poorly. They might all three argue. The play would be about the relationship between three characters not two characters if the Old Man were to join them in the motel room. As it stands, the play is about Eddie and May's relationship with the Old Man providing some insight. We know very little about the relationship between Eddie and the Old Man or May and the Old Man after the play is over. Were he to be a real character in the motel the play would change by revealing more about these characters relationships with the Old Man rather than about the relationship between two lovers who happen to be siblings. The Old Man is probably far away, if not dead in the reality of Eddie and May's world and the play would not be the same were he to appear realistically through the door.
Are the themes of the play universal even though the story is about a dysfunctional family?
The themes of Fool for Love are universal though the incestuous and dysfunctional nature of the relationships are not. For instance, all people can relate to feelings of vulnerability and loneliness when left alone or even abandoned by a loved one. May experiences abandonment to a high degree and in an extreme situation but her emotions of loss are universal. Likewise Eddie's repeated behavior, a cycle of abandonment and return, can be understood by most people. Perhaps through divorce or death, aging, or special circumstances many people experience loss, change, and a desire for things to return to the way they were before a traumatic event occurs. Even if they have never had a loved one absent for long, even small periods of loss can arouse fear and sadness. May and Eddie cannot live with or without each other. Both feel that one has abandoned the other. Their particular circumstances, and specific experience of their past makes their story exceptional, but the emotions May and Eddie feel as a result of their actions speak to the humanity of us all.