Mercy vs. Justice. Allusion to justice = eye for eye, tooth for tooth [measure for measure]; allusion to mercy = let him without sin cast the first stone [esp. sexual sin].
Duke wants to restore the strictness of fornication/adultery laws. He sets up Angelo to do it, while he feigns that he will be away. Instead he remains to check up on Angelo and the town (Vienna). Angelo goes ahead and closes down Overdone’s brothel and the others, and puts Claudio in jail, condemned to die the morrow, for impregnating Juliet.
Isabella, Claudio’s sister and about to enter a nunnery, pleads for Angelo’s mercy on him. Lucio counsels her to be warm to him, and she is just warm enough to inspire Angelo to seduce her: seduction in exchange for Claudio. The Duke, posing as a Friar, overhears her exchange with Claudio in which he counsels her to go through with the act. He enters and sets up a plan: Angelo ought to have married Mariana but didn’t: Mariana therefore will go in Isabella’s place.
Angelo, after the deed, calls even more quickly for Claudio’s head. The Duke (as Friar) puts this off: now Angelo is two steps behind (not knowing about either Mariana or Claudio). The Duke returns, as Duke, and asks for anyone against Angelo to speak. Isabella does: finally it comes out that the Friar was behind Isabella’s suit. The Friar is called for, and so the Duke disappears and comes back as the Friar, but is revealed to be the Duke. The switch is revealed and Angelo must marry Mariana; Claudio is revealed as alive and is pardoned by the Duke. Lucio (a subplot) also gets his deserts.
Morality: mercy wins over justice, and yet there is a strong sense of justice having been done. Symbolically accomplished by the Duke (justice) taking on the habit of “a true friar” (mercy but with sense of justice) starting with I.iii.48.
II.i.17 ff, Angelo on justice without mercy: “‘Tis one thing to be tempted, Escalus,/Another thing to fall. I not deny,/The jury, passing on the prisoner’s life,/May in the sworn twelve have a thief or two/Guiltier than him they try. What’s open made to justice,/That justice seizes: what know the laws/That thieves do pass on thieves?”–this is unmitigated justice, just as II.i.30-31: “Let mine own judgement pattern out my death, [which Angelo is willing to accept once caught, in V.i.371]/And nothing come in partial. Sir, he must die.” And also cf. II.ii.81-83 and V.i.474. The Duke plans to hold Angelo to it in III.ii.260-63 and in V.i.407 ff. (eye for eye, “Measure still for Measure” in line 409).
Escalus explains one aspect of why justice is necessary in II.i.85 ff.: “Pardon is still the nurse of second woe”; Angelo seconds this in II.ii.101 ff: “I show it [pity] most when I show justice;/for then I pity those I do not know,/Which a dismiss’d offence would after gall;/And do him right that, answering one foul wrong/Lives not to act another.” This may be the idea behind Mariana’s statement in V.i.437-38: most men “become much more the better/For being a little bad.”
Lucio: the “go for it” morality, I.iv.77-79 — Lucio counsels a wrong action with the right idea: our fear of adverse consequences might keep us from taking the good action. Same as Duke (as Friar), III.i.209: “Virtue is bold, and goodness never fearful.”
Froth: puts forward notion that he is good, but that an external force draws him to the bad, II.i.110-12: “For mine own part, I never come into any room in a taphouse, but I am drawn in.” But others work from the notion that everyone commits sexual sin: e.g. Pompey, II.i.231 ff, Provost, II.ii.5, Lucio, III.ii.103, even Angelo II.iv.121,123 when trying to seduce Isabella (but Angelo and the Duke think they can cut down on it with deterrents of punishment). Also cf. Isabella’s similar pleas, II.ii.63-66 and II.ii.137 ff. Related to this is the ‘he who is without sin’–the notion that the sins of the judge justify mercy about the sins of the judged, II.ii.176-77–this spoken by Angelo once he falls for Isabella, in passion, (but then cf. II.iv.15-17: “Blood, thou art blood:/Let’s write good angel on the devil’s horn,/’Tis not the devil’s crest”) and spoken more forcefully by the Duke at IV.ii.108 ff., IV.ii.59 ff., and V.i.108 ff. (this last being aligned with reason). Franklin, “On Censure or Backbiting”: he who will always “excuse and palliate the Crimes of others, may rationally be suspected to have some secret darling Vice, which he hopes will be excused him in return,” Lemay 195. Is this not the situation of the Duke, and the reasoning of these others?
The difficultly of remaining without sin “when once our grace we have forgot”: the Pauline words of Angelo “we would, and we would not!” at IV.iv.34-35.
Claudio: the virtue of a necessary sin (see also All’s Well III.vii: “lawful deceit,” “lawful meaning in unlawful act”), III.i.131-133: “What sin you do to save a brother’s life,/Nature dispenses with the deed so far/That it becomes a virtue.” The Duke says as much to Mariana at the end of IV.i: “[fear not (be bold as virtue is bold) and] ’tis no sin,/Sith that the justice of your title to him/Doth flourish the deceit [and indeed the time is ripe]”, and likewise in V.i.533: “Th’offence pardons itself.” And compare Pompey as the “lawful hangman” in IV.ii.
But Isabella disagrees: her morality comes from spirit and truth, III.i.206-08: “I have spirit to do any thing that appears not foul in the truth of my spirit.” She recognizes, as does Angelo, that Claudio ought to be punished, but tempers her justice with mercy.