It doesn't take long for audiences to figure out that Angelo is the biggest hypocrite ever. An uptight deputy who's left in charge of enforcing Vienna's laws, Angelo sentences Claudio to death for the crime of "fornication" and then turns around and propositions an apprentice nun. What's worse, Angelo attempts to hide his own faults while pointing out (and handing down punishment) for the faults of others.
So, what is it, exactly, that causes this seemingly righteous guy to fall from grace? There are a couple of answers to choose from. Literary critic Jonathan Bate argues that Angelo is excited by Isabella's "mind and tongue at work." In other words, Bate thinks Angelo gets all hot and bothered by the fact that Isabella is so well-spoken.
Other literary critics (like Janet Adelman, for example) see things differently. They suggest that Angelo is turned on by Isabella's virginity. If you like this explanation, then you'll probably want to take a look at the following passage, which supports the argument:
Dost thou desire her foully for those things
That make her good? O, let her brother live.
Never could the strumpet
With all her double vigor, art and nature,
Once stir my temper, but this virtuous maid
Subdues me quite. Even till now
When men were fond, I smiled and wondered how. (2.2.211-212; 220-224)
Here, Angelo reveals that he's attracted to the things that "make [Isabella] good" (her virtue) and that he's never before been turned on by women (especially promiscuous women).
We also notice that Angelo is pretty introspective and self-aware. In fact, he seems like one of the few characters that can self-analyze in an honest way. This is especially clear when Angelo acknowledges that Isabella is innocent of any wrongdoing:
What's this? What's this? Is this her fault or mine?
The tempter or the tempted, who sins most, ha?
Not she: nor doth she tempt; but it is I
That, lying by the violet in the sun,
Do as the carrion does, not as the flower,
Corrupt with virtuous season. (2.2.199-204)
Now, this is interesting. Angelo reveals that he sees his sexual desire as something "corrupt." In this passage, he compares his lustful body to carrion (road kill) rotting in the sun. (This is similar to how Hamlet compares a pregnant – and therefore inherently sexual – woman's body to a "dead dog" that "breeds maggots" while rotting in the sun [Hamlet, 1.2.136-150; 161-164].) Yuck.
Although Angelo is introspective and honest with himself, he continues to be deceptive in his interactions with other people. So, it's not surprising to us that Angelo is frequently compared to a counterfeit coin throughout the play.
Here's where the connection between coins and Angelo begins. (Angelo's name, by the way is associated with the "angel" or "nobel-angel," a type of gold coin bearing the image of the archangel Michael.)
Now, good my lord,
Let there be some more test made of my mettle
Before so noble and so great a figure
Be stamped upon it. (1.1.51-54)
When the Duke announces that Angelo will be his deputy, Angelo likens himself to a metal coin that should be tested for its value and worth. According to Angelo, he has yet to prove that he has the substance or worth (mettle) to be the Duke's deputy. (In sixteenth-century England, "metal" and "mettle" were used interchangeably). When Angelo says there should be some test of his metal, he's making a reference to how, in the sixteenth century, a coin's value was based upon the value of the metal from which it was made.
As we know, Angelo turns out to be a corrupt deputy, which is why Escalus suggests that he's a lot like phony coins:
I am sorry one so learnèd and so wise
As you, Lord Angelo, have still appeared,
Should slip so grossly, both in the heat of blood
And lack of tempered judgment afterward. (5.1.540-543)
Using the language of minting coins to describe Angelo's bad behavior, Escalus points out that Angelo appears to be golden on the outside but remains corrupt on the inside. Escalus also plays on the word "slip," which literally means "to make a mistake," but it's also the name for a counterfeit coin.
Shakespeare also plays on Angelo's name in the sense that an "angel" is a celestial being. There's nothing angelic about the corrupt deputy but, throughout Measure for Measure, Angelo is described as a kind of non-human or other-worldly being. The clearest example of this is in the passage we've already looked at, where Angelo admits that he's never before experienced the most basic of human desires (lust).
Elsewhere, this becomes a bit of a joke when Lucio spreads a rumor that Angelo is the impotent "spawn" of a mermaid and urinates ice:
Some report a sea-maid spawned him; some,
that he was begot between two stockfishes. But it is
certain that when he makes water, his urine is
congealed ice; that I know to be true. And he is a
motion generative, that's infallible. (3.2.109-113)