The characters in The Chairs are totally alienated. Though the Old Man and Woman have spent their lives together, they both still feel alone. They try to come together through the creation of joint fantasies, but even these ultimately fail them in the end. The theme of isolation is seen quite often in the Theater of the Absurd. This type of theater is said to be inspired by the philosophy of Existentialism, which states that all human beings are inherently alone. According to the Existentialists, we are all alone in an unknowable universe. The only way we can bring meaning to our lives is to take responsibility for our own actions and to decide for ourselves what is meaningful.
The old couple's isolation is a comment on the isolation of all humanity.
The fact that the old couple's bodies will be separated in death suggests that we all die alone.