Dramatic irony and the plague
How horrifying was the plague to the people of Europe? Well, they call it the "Black Death," which is pretty dark. That is because of dramatic irony. Without a scientific explanation for why a plague could randomly infect and kill so many people, the people are left without any concrete explanation. Their imaginations go to the darkest, most horrifying depths. The storytellers in this novel are clearly examining their ability to speculate about doom or judgment, and the stories are dark in tone, except when they turn funny for comedic relief.
Prayer and irony
When seven young women band together for a prayer meeting in the town church, they pray for God to save them from the plague. They pray for some divine salvation, but then suddenly, Pampinea reminds the gals that actually, they could run for their lives. That resource is still available to them. The outcome of the prayer is ironic, because by escaping the rats and fleas in Florence, they actually do improve their odds of survival, but by seemingly ordinary methods. The prayer can be seen as answered, by a timely good idea.
The irony of churches
There is a confusing coincidence in the novel. Why do these young people spend so much time in churches? The novelist meets them in a church, praying for salvation, and the novelist directs them to refuge in a more agrarian area, but still in a church. They tell horror stories in church. They play king and queen in church. One might even say they are making the best of their time together—perhaps they are even partying in the church. The safety provided by the church building helps them to deal concretely with the intensity of their threat.
The royal irony
The seven women and three men are a useful symbol for humanity as a whole. First of all seven and three are pretty famous numbers in the church (the novel is often set in church). The irony of royalty is simply that without being told to do so, the young people automatically start taking turns being in charge. Their game is an exposé of human nature. In church, they feel connected to some sort of divine royalty, and they take turns examining what each pair of king and queen might be like. It is like a dating game, very similar to a formal dance.
Humor and irony
The tension of darkness and horror fits the severity of the circumstances, so naturally, when the ten players start telling stories, the stories are often scary. This shows that they are expressing their own emotional experience in their stories. Then occasionally, a person will break the tension with a riotous story of hilarious hijinks and pranks. The emergence of humor from horror is well-documented in literature. Everyone knows what it that feels like, in a way, but it is one of the greatest ironies. When late night shows make jokes about horrifying political news, that is the same ironic release.