There are, I think, two issues beneath the Duke’s refusal to show this foolish and generally harmless fop any leniency. The first is that the Duke’s power (including when he is playing the Friar) manifests primarily in the realm of the verbal; his execution of his plans for reviving his subjects’ proper fear of him means reviving their fear of his words, his decrees. And while Isabella, Mariana, the Provost, and others are willing to implicitly trust the Friar (and the Duke’s words through him), Lucio constantly mocks the Friar’s reverence for the Duke, and impugns his character in all sorts of outlandish and offensive ways. Complaining of Angelo's overly strict adherence to the laws of the state, Lucio compares him to the absent Vincentio:
LUCIONote that while the Duke warns Lucio against the danger of his careless libeling, the real problem is, I think, Lucio's assertion that he knows the Duke and what drives him - and tells others what the Duke would and ought to do; he usurps the Duke's linguistic prerogative by ventriloquizing his decrees during his apparent absence. Indeed, at the play's conclusion, when Vincentio argues, reasons, and asserts his royal prerogative against Angelo and others who have committed crimes, he does so particularly against their presumption in speaking his power with their mouths – even when, in Angelo’s case, it was directly bestowed upon him by the Duke in the first place, who has, in a truly ominous turn of phrase, "lent him our terror" (I.i.19):
Why, what a ruthless thing is this in him, for the
rebellion of a codpiece to take away the life of a
man! Would the duke that is absent have done this?
Ere he would have hanged a man for the getting a
hundred bastards, he would have paid for the nursing
a thousand: he had some feeling of the sport: he
knew the service, and that instructed him to mercy.
I never heard the absent duke much detected for
women; he was not inclined that way.
O, sir, you are deceived.
'Tis not possible.
Who, not the duke? yes, your beggar of fifty; and
his use was to put a ducat in her clack-dish: the
duke had crotchets in him. He would be drunk too;
that let me inform you.
You do him wrong, surely.
Sir, I was an inward of his. A shy fellow was the
duke: and I believe I know the cause of his
What, I prithee, might be the cause?
No, pardon; 'tis a secret must be locked within the
teeth and the lips: but this I can let you
understand, the greater file of the subject held the
duke to be wise.
Wise! why, no question but he was.
A very superficial, ignorant, unweighing fellow.
Either this is the envy in you, folly, or mistaking:
the very stream of his life and the business he hath
helmed must upon a warranted need give him a better
proclamation. Let him be but testimonied in his own
bringings-forth, and he shall appear to the
envious a scholar, a statesman and a soldier.
Therefore you speak unskilfully: or if your
knowledge be more it is much darkened in your malice.
Sir, I know him, and I love him.
Love talks with better knowledge, and knowledge with
Come, sir, I know what I know.
I can hardly believe that, since you know not what
you speak. But, if ever the duke return, as our
prayers are he may, let me desire you to make your
answer before him. If it be honest you have spoke,
you have courage to maintain it: I am bound to call
upon you; and, I pray you, your name?
Sir, my name is Lucio; well known to the duke.
He shall know you better, sir, if I may live to
I fear you not. (III.ii.108-55)
DUKEThe Duke temporarily silences himself by pretending to leave precisely to reaffirm the inviolability of his linguistic and royal power. The Duke's terror may be lent but never possessed by another; his words may be used by others but not only will such usurpers not benefit from those borrowed or stolen words, they will be punished for the presumption even when (as in Angelo's case) they are compelled to do so!
Sith 'twas my fault to give the people scope,
'Twould be my tyranny to strike and gall them
For what I bid them do: for we bid this be done,
When evil deeds have their permissive pass
And not the punishment. Therefore indeed, my father,
I have on Angelo imposed the office;
Who may, in the ambush of my name, strike home,
And yet my nature never in the fight
To do in slander. (I.iii.35-43)
Lucio is not the only subject guilty of linguistic presumption, so why is he the only one shown not only no clemency, but subjected to punishment so much more extreme than his crime could possibly seem to warrant? I submit that it's not actually that he so gleefully indulges in assassinating the Duke’s character, or even in claiming to know what the Duke might say, but rather in correctly identifying the Duke’s mad methods, motivations, and royal decrees. Angelo uses and abuses the power briefly borrowed, but he never comprehends it; Claudio's crime is one of the body, a crime that in itself doesn't truly destabilize the Duke's power.
On the other hand, when Lucio concludes near the end of the play that “if the old fantastical duke of dark corners had been at home, [Claudio] had lived" (IV.iii.156-57), he hits the mark in two ways. First, obviously, he’s right to insist that the Duke would not punish Claudio for something so human as desiring to make the beast with two backs with his beloved – especially given that their marriage is being unreasonably delayed by Juliet's family for no socially sensible reasons.
Secondly, and more dangerously, Lucio astutely notes that the Duke is both secret and savvy; he understands the Duke to govern at least in part through covert means and tricksy wordplay. For Lucio, the Duke is not mysterious and therefore not, in the older sense of the word, awful – and he ought to be. Without awe, the Duke’s linguistic control is greatly diminished, if not irreparably destroyed. The Duke’s dark corner methods are darker even than Lucio realizes and he pays, but not actually for misunderstanding the depths of the Duke’s Machiavellian machinations - but, rather, for detecting them at all. The success of the Duke’s fantastical exercising of his power relies on the mechanism being entirely mysterious to his subjects. The mystery of the mechanism is a much darker and more forbidding thing to contemplate in Measure for Measure than it is in Martin Chuzzlewit because for Dickens, the mystery is perhaps benevolent and divine; in Measure for Measure, it is deliberate, ruthless, and serves no purpose higher than the cold exercise of human might.
At the play's conclusion, it seems the Duke’s plan to use Angelo as a patsy to re-establish the terrible fullness of his power without harming his own reputation has been entirely successful, for the only figure to threaten his reign with comprehension of how it functions has been sentenced to death and none speak up against Lucio's sentence. And yet, the Duke's assertion of his right to marry the appalled Isabella is not met with prompt and absolute obedience. She has, on the astute Lucio’s urging, temporarily removed herself from the cloister she’s determined to spend her life in, to try to convince Angelo to show her brother mercy and not sentence him to death. This leads to the successful realization of all the Duke’s plans for catching Angelo at his hypocritical moral posturing, to release Claudio without appearing to be soft, and to help Mariana to the husband she deserves. By all rights, Isabella should be allowed to return to the life she has chosen; instead, the Duke re-enacts Angelo’s complete disinterest in her desires in the matter of her life's course and commands her to accept him as her husband:
DUKEIn spite of the Duke's order here (made more irresistible by its terrible reminder of how precarious is her brother's safety in his hands), Isabella does not appear to comply, and the Duke is forced to ask her for her hand again as the actors leave the stage:
[To ISABELLA] If he be like your brother, for his sake
Is he pardon'd; and, for your lovely sake,
Give me your hand and say you will be mine.
He is my brother too: but fitter time for that. (V.i.488-91)
DUKEAnd still Isabella remains silent. The Duke's second proposal is more persuasively worded, and appeals to a more companionate model of marriage, but it's clear that she does not willingly her ear incline to him. Silence might be interpreted as consent in some situations, but here it clearly expresses consent withheld. And indeed, in the face of the Duke’s linguistic manipulations, silence is and can be Isabella's only form of resistance in a world of linguistic, Machiavellian trickery.
I have a motion much imports your good;
Whereto if you'll a willing ear incline,
What's mine is yours and what is yours is mine.
So, bring us to our palace; where we'll show
What's yet behind, that's meet you all should know.
The meaning of her quietness, after five acts of loquaciously doing the his and Lucio’s bidding to help restore social order, cannot be lost on the savvy and observant Duke. Vincentio's perfectly neat, Comedic last words scurry around with no place to land because of her refusal to comply with his publicly expressed terms of their union. The Duke, it seems, will have to find even darker corners to lurk in to solve this problem called Isabella...