In the final trial of Measure for Measure (in Act 5), the Duke as the presiding judge condemns Angelo for the death of Claudio and imposes the death penalty. He summarizes his judicial reasoning when he proclaims (alluding to the name of the play):
The very mercy of the law cries out
Most audible, even from his proper tongue,
"An Angelo for Claudio, death for death."
Haste still pays haste, and leisure answers leisure;
Like doth quit like, and measure still for measure.-- (5.1.463-7).
What kind of argument is he making? Is this a key idea of the Duke's jurisprudence or is he trying to mock it (after all he does pardon Angelo later in the scene)? Does the play make a comment on this kind of judicial reasoning? What is the measure of "measure for measure"?