In Scene 4, after Cauchon describes the threat Joan poses to the Church, Warwick lays out the feudal lords' case against her. He uses a metaphor to explain the "nominal" power of the king and the real power of the feudal lords, but his explanation contains situational irony:
Nominally we hold our lands and dignities from the king, because there must be a keystone to the arch of human society; but we hold our lands in our own hands, and defend them with our own swords and those of our own tenants.
Warwick compares the king to "a keystone to the arch of human society." A keystone lies at the top of a stone arch. Wedge-shaped, it snuggles between the rest of the stones and locks them into place so that the arch won't fall. Calling something a keystone usually emphasizes its importance, but Warwick uses the metaphor a bit differently. He admits that the king holds human society together because someone has to. Still, he suggests that the king's power to distribute land is more "nominal" than anything—it is for show, so no one gets upset and demands to know why feudal lords have land while the tenants who work for them do not. He claims that "we [the feudal lords] hold our lands in our own hands." The metaphor of the king as the keystone in the arch of human society slides into the idea that the feudal lords hold up the whole world and do not need the keystone except for show.
It is ironic, though, that he insists on the feudal lords' self-sufficiency given the rest of his sentence. He claims that "we defend [our lands] with our own swords and those of our own tenants." Warwick thinks of the tenants and their swords as an extension of his property. To Shaw's audience in the 1920s, this is obviously not the case. It is not that the lords are defending their land with their tenants' swords, but rather that the tenants are defending their lords' property with no thanks except for their continued ability to live there. Lords build their wealth, and tenants put their lives on the line. It is ironic that Warwick thinks he and the other feudal lords don't need any help given that the current system relies heavily on help from the lowborn who are really holding up the arch of society.
In the Epilogue, after the Church has cleared Joan's name, she and all the men who condemned her appear to Charles VII in a dream. In a twist of situational irony, despite all their praise for Joan in the dream, none of the men want to see her brought back to life:
JOAN. [...] And now tell me: shall I rise from the dead, and come back to you a living woman?
A sudden darkness blots out the walls of the room as they all spring to their feet in consternation. Only the figures and the bed remain visible.
JOAN. What! Must I burn again? Are none of you ready to receive me?
Joan, still as earnest as she was in life, believes what she hears when the men praise her. They have all been speaking about her as though she is Christ himself, suffering for the sake of everyone else. She draws the logical conclusion: because everyone has agreed that she should not have been burned, she will now get a second chance at life, just like Christ. The sudden "consternation" of all the men demonstrates that once again, Joan has missed the reality of the situation. Whereas their newfound reverence for her ought to mean that they want to see her alive again, instead they want credit for praising her without having to cooperate with her again. These men, just like the Church leaders who finally canonized Joan in the 20th century, are hypocrites. They offer Joan too little too late and want it to mean something. Shaw uses this dream sequence in the epilogue to invite his audience to laugh at the irony of honoring someone after they are dead.
