The Irony of Willie's Death
Willie leave dinner one night because he's feeling ill. After a consultation with a doctor, he's told he has a cold. When he dies in just a few hours, he and everyone around him are shocked. The merely quickness of the typhoid fooled even the doctors.
The Irony of Abraham's Hug
Abraham, like a normal grieving parent, leans in to hug his son's body at the cemetery. He believes nothing will happen from this interaction, but it is a normal part of human psychology. When Willie and his companions notice the hug, however, they start talking about a possible resurrection for the boy. In a sense Lincoln's hopeless gesture of grief lends hope and inspiration to his dead son.
The Irony of Hans and Roger's Help
Hans and Roger adamantly encourage Willie to pass on into the Afterlife for fear he will not be able to later. Their urgings are ironic, however, because they have no intentions of themselves moving on. They remain stalwartly attached to their lives.
The Irony of Abraham's Death
Willie devotes his whole stay in the Bardo to trying to reunite with his father. He's trying to form a connection between the two so that he -- the son -- may join his father once more among the living. Ironically, the bond is obtained, but Abraham is the one crossing over, joining his son in the land of the undead.
The Irony of the Title
For a story named after Abraham Lincoln, this novel focuses very little upon the president. Willie Lincoln becomes the centerpiece of the drama, the protagonist and narrator. His story serves as the primary drama, relegating Abraham to subplot. This inversion of expectation plays upon the expected infamy of the name Lincoln.