In a confrontation at the gates of the city, the duke reveals the truth and administers merciful justice to all.
Isabella accuses Angelo, but Mariana comes forward to claim that she was with him herself. The duke charges the two, along with Friar Peter, with being persuaded to their accusations by the absent Friar Lodowick (the duke). He leaves their case to Escalus and Angelo, exiting to return shortly, disguised again as a friar. Lucio accuses him of slanders against the duke and is helping to lead him off to prison when his hood comes off revealing the duke.
The duke then deals quickly with the cases at hand. He orders Angelo married at once to Mariana and then sentences him to death. Isabella pleads on his behalf, but the duke seems impervious. He has the provost bring out Claudio (his face covered) and Barnardine. The latter is pardoned, and when the former is revealed, the duke pardons both Angelo and Claudio. Threatening Lucio with whipping and hanging, the duke lets him off with marriage to the whore he has got with child. He promises a higher office to the provost for his services and tops off the scene by asking for Isabella's hand in marriage.
This last scene is a lengthy one that might have been substantially shorter had the duke gone directly to the matter, simply explaining his disguise, the crimes he has witnessed, and going about the administration of justice. The scene, however, would have been less effective. As it is, Shakespeare builds suspense by leaving the characters of the play and its audience in doubt as to the outcome. He emphasizes his presentation of Christian mercy by having Isabella plead for Angelo while still under the impression that he has executed her brother. And he creates a mildly comic scene to finish a play that might have ended in tragedy and that would certainly have had a rather flat finale if the duke had simply narrated his part and doled out his punishments.
A comic undertone is provided by the audience's knowledge of the duke's identity. In his disguise, he alludes to it ironically: "The duke / Dare no more stretch this finger of mine than he / Dare rack his own" (315-17). Later, he protests to loving the duke as he loves himself. Lucio's accusations against the friar-duke made to the duke himself provide further comedy for the audience, which knows what the actor does not. When Claudio is revealed to be still alive, the duke's speech to Isabella has a gentle and sympathetic humor that any audience would surely warm to: "If he be like your brother, for his sake / Is he pardon'd" (495-96).
In this final scene, the theme of merciful justice comes to the fore. The duke seems ready to deal harshly with Isabella, Mariana, Friar Peter, and Friar Lodowick, and to apply the letter of the law in the cases of Lucio and Angelo. The mercy that he finally shows to all contrasts sharply with the rough hand of the law that he at first threatens.
"An Angelo for Claudio, death for death!" he cries; "Haste still pays haste, and leisure answers leisure; / Like doth quit like, and Measure still for Measure" (414-16). Some critics have found fault with the duke and Shakespeare for letting Angelo off with little more than a warning for his heinous crime. Critics who interpret Angelo as a thoroughly evil man (not a fallen man of virtue) find his marriage to Mariana repellent. But, in fact, there is a certain ironical justice in the conclusion of his case. His crime is, after all, one of intent only; his intention was the rape of Isabella, but instead he went to bed with a substitute. For punishment he receives the duke's intent of execution, and only marriage with the substitute, in fact. An intended crime meets with an intended punishment, or measure for measure.
The duke, once revealed, tells Isabella that he could not prevent her brother's death because of the short time involved, thus reiterating his claim that her brother is dead. While she might otherwise have assumed that the duke had spared him, she still believes, when Mariana asks her to plead for Angelo, that he has been the instrument of her brother's execution. She remains silent through two lengthy pleas from Mariana, apparently struggling with her conscience, but finally makes her decision and pleads eloquently for Angelo's life. She does the Christian thing that she earlier asked Angelo to do on behalf of her brother: Judge not, that ye be not judged. She has said that if their positions were exchanged--if he were the supplicant and she the judge--she would show him mercy, and here she proves true to her word. In another earlier scene (II. i. 29-31), Angelo stated that, guilty of Claudio's crime, he would ask for the just penalty of the law, and he too lives up to his claim. Here in the last act, "No longer session hold upon my shame, / But let my trial be mine own confession: / Immediate sentence then and sequent death / Is all the grace I beg" (376-79). And again, "I crave death more willingly than mercy; / 'Tis my deserving, and I do entreat it" (481-82).
Ironically, earlier in this act, the duke seemed to disbelieve Isabella's charges against Angelo, commenting, "If he had so offended, / He would have weigh'd thy brother by himself / And not have cut him off" (110-12). While he did not judge Claudio by himself, Angelo now asks the duke to judge himself by Claudio's fate.
The sincerity of Angelo's repentance has been called into question but seems true enough in the light of the evidence. The man does, in fact, ask, not once but twice, for the full measure of the law. Isabella herself, in asking mercy for the man, is moved to say, "I partly think / A due sincerity govern'd his deeds, / Till he did look on me" (450-52). His victim is willing to believe that his act was no more than a temporary fall from virtue. She even echoes his own words in an earlier scene (II. i. 17-18) in pointing out that his crime was one of intent only: "Thoughts are no subjects; / Intents but merely thoughts" (458-59).
In any case, a pairing off of characters in the final scene was a convention of the time. Likewise, the marriage of a wronged maiden to a repented villain was a customary ending for an Elizabethan drama. The marriages of Mariana to Angelo, Juliet to Claudio, and Lucio to his whore offer a socially acceptable solution and one that Shakespeare's audience would have viewed with approval.
The duke has been attacked for the purportedly vicious justice he metes out to Lucio for the latter's slanders against him. The man who has excused crimes of the magnitude of Angelo's deals harshly with Lucio for his assault on the duke's vanity. A careful reading, however, will answer these charges (524-26). As with Angelo, the duke only pretends to sentence Lucio to whipping and hanging. From these he is excused, with marriage to a whore as his only punishment. For slanders against the duke, he is pardoned; only the crime against the whore is punished. Lucio is, in fact, let off rather easier than the rest since in the other cases a measure of repentance is met with a measure of pardon, while Lucio receives his pardon without the return of repentance.
Even in this last act, Lucio is still up to his old trick of shifting allegiances to play off one person against another, taking his humor from the dilemmas of those around him. Isabella herself is made an object of his malicious gossip when he contributes to the case against her by reporting to have seen her with "a saucy friar, / A very scurvy fellow" (135-36).
Isabella's detractors scorn her for marrying the duke after making so much of her Christian commitment earlier, but the fact is that the author has made it clear that Isabella has not yet taken vows. She is, in fact as well as in conscience, still free to marry. Further, she does not give the duke an answer to his proposal, so the final resolution is left to the audience.