The innocent messenger
Although the novel is about Homer reaching adult maturity, he does so after a lengthy stint as the bearer of bad news. The irony is that he is heading toward the moment when he receives the news that Marcus, his older brother has died in war, and he always knew that such news might be coming, but it isn't until he finally learns the news for real that he is forced to understand what it feels like to get those letters that he has been delivering.
Helen, the crush
Helen is an ironic symbol in the story, because Homer wants what he can't have. As her name illustrates, she is a symbol for male competition, because she might change her mind if Homer could impress her. He is attracted to the way in which she causes him to prove himself, but ironically, he likes her more knowing that he will have to win her over from another man. It seems counter-intuitive, but it is literally what the name "Helen" has signified for thousands of years.
The paradox of optimism and pessimism
When the boys go to the grocery, they chat with the two owners, one of whom is an optimist, the other of whom is a pessimist. To Homer and Ulysses, this represents a deep irony about one's attitude, because obviously emotions are responses to external reality, but the difference between Mr. Ava and his business partner are proof that there is some choice in the matter. They are not completely enslaved to external forces; they can choose their attitude.
Marcus's death
Marcus's death is ironic because it leaves the young boy Homer as the eldest man in the story, and it comes with little surprise (after all, Homer delivers death notices for his daily income), but still the effect is staggering and unpredictable. This is a reminder of the ironic power of experience, versus innocence, because although he knew about loss, there was nothing to prepare him for the full weight of loss.
Tobey's consolation
Tobey is offered to the family almost as a fateful consolation. They lose Marcus, but they gain Tobey, and the trade is bittersweet. Nothing could replace the void left by Marcus, but Tobey's consolation allows the family to experience real catharsis by expanding their sense of family to include the community, which is another major theme of the book. Tobey is proof that they are all one big family in this small town.
