Peter's Irony
Peter believes that freedom of expression should be suppressed in a time of crisis, but the crisis is one of his own making, if a crisis at all. It appears absurd that he paints Stockmann out as a villain and destroyer of the town when Stockmann wants to save it.
Stockmann and the truth
The audience knows Stockmann is correct and that in the future more and more people will become sick, so irony is seen in the townspeople's reactions to him. They appear ridiculous and ignorant, spending time and effort fighting against something that is not actually valid.
Hovstad
Hovstad purports to be one of the most radical men of the town but is one of the fastest to turn over to Peter's perspective. His words about rich and reputable men controlling everything rings true, because they can even get to Hovstad, the self-proclaimed radical.
