Justice in Measure for Measure can be described as poetic justice in that everyone gets their just desserts. Indeed, the very title of the play strongly implies that what goes around comes around.

In cases where it is plainly obvious that individuals have ridden roughshod over the rights of others—as in the case of Angelo—then judges can follow the strict letter of the law and punish accordingly. Even so, it is notable that the duke departs from the letter of the law in deciding to sentence Angelo to marry the woman he abandoned when it became clear that there was no possibility of getting his greedy hands on a dowry.

In that sense, one could say that the play, in its conclusion, presents us with justice as both the letter of the law and the law’s spirit. In the end, in the sentencing of Angelo, it is the spirit that wins out.

In Measure for Measure, when should judges modify or qualify strict legal interpretation?

Measure for Measure suggests that judges should modify or qualify the strict letter of the law when failing to do so would clearly lead to an outcome contrary to natural justice.

The play depicts a city filled with corruption and disease, in which it is clear that the law has not been applied for some time. The duke's solution to this is to appoint Angelo, apparently a man of strict probity, to punish wrongdoers with a new severity. Unfortunately, the case to which he first chooses to apply the strict letter of the law is not one which merits such treatment. Claudio and Juliet are effectively man and wife. As Claudio himself puts it:

You know the lady; she is fast my wife,
Save that we do the denunciation lack
Of outward order: this we came not to,
Only for propagation of a dower
Remaining in the coffer of her friends.

Claudio, therefore, is condemned to death on a legal technicality, while all around him, Vienna teems with fornication, adultery, and prostitution. This injustice is as injurious to the rule of law as Duke Vincentio's laxity, since it makes the law appear capricious and arbitrary. Claudio's case would have been an ideal one in which to modify the letter of the law and show mercy, but Angelo is too rigidly puritanical to acknowledge this.