What is the main idea of the play All My Sons by Arthur Miller? By that I mean what is the play about in one sentence or the core of the play.

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e-martin eNotes educator| Certified Educator

We might summarize the comment the play is making in a number of ways. One way to phrase the "core" of the play is to say "Miller's play suggests that those aware of the truth are responsible for it". 

We see this notion carried out as Chris and Ann remain aloof regarding the truth about the faulty airplane parts, perhaps purposefully, and so remove themselves from responsibility for most of the play.

Kate, Joe and George, however, are all aware of the truth and so also are driven and defined by it. In the end, all the characters become both responsive and responsible for the truth and its consequences. 

The revelations that lead up to Joe's tragic recognition of guilt and his suicide, the final consequences of his choice, are essential to All My Sons. There is a sense of anake, or tragic necessity, that moves the work along towards its inevitable moment of truth and awful but final retribution.

Other articulations of the play's core might be: 
  • "Relationships are tested according to their honesty." 
  • "Moral responsibility is socially defined and socially enforced, but individually felt." 
  • "Ultimately, one cannot escape the truth."