I think that both John Proctor and Mary Warren establish their respective positions of credibility in different ways. Mary establishes her credibility with the people on the "jury" in a contingent manner. She demonstrates anxiety and panic in court that feed the public's belief that evil lurks in the town and that the work of the devil is at hand. The fact that Mary is a servant, one of the people, and represents the "common person." This is what gives her credibility with the townspeople for she is one of them. However, it is this very validation that represents an actual demerit of credibility. Mary only serves to confirm the emotional contagion and public hysteria present. Her credibility is one of contingency. On the other hand, Proctor establishes his credibility in a transcendent manner. He stands up for a transcendental quality that defies the contingency of the time period. His credibility is one that resonates with the audience, and not the setting. When Proctor is sent to death, rejected by the townspeople, his credibility is actually higher because he himself appeals to a higher sense of the good. It is in this depiction that Miller is suggesting that what is contingent might not represent what should be and what should be might not be what is.