What is the irony in the Crucible?

The most ironic part of the Crucible for me is when Elizabeth Proctor lies about her husband's adultery. Everything we know about Elizabeth would make this seem impossible, it isn't at all in tune wikth what we know of her, and yet she does lie.

Another bit of irony would be found in Proctor's adultery. He loves his wife, he's extremely honorable, and he is a pillar of the community. His reputation is all important, but regardless of his pride or reputation, he puts himself at risk for a fling with a young woman.