The irony of family value
The idea that a family should be honored by sacrifices from each person is implied in Mervyn's behavior, which destroys his family. Ironically, the author suggests that the real reason they wanted their father to be a responsible, disciplined person of deliberate joy, instead of maintaining his dependency on alcohol, is to make his own life better. Mervyn's life lacks meaning that only sacrifice can attain.
The irony of travel
There is a kind of situational irony that comes when scenery shifts around a person. This irony is evident in the differences between Canadian life, which is properly Western and deeply European, and life in Sri Lanki, where completely different principles apply, culturally speaking. Ironically, this memoirist travels back to his country of origin, but Canada is his home.
The irony of family duty
By nature, one expects a certain kind of narrative in generational stories: The father sacrifices for years so the son has a better chance at life, and the son takes the torch and runs with it. This story is ironically opposite of that. Mervyn pretends he was accepted to college so his parents will fund his move to the city, where he spends their money not on tuition (he was never accepted to a college) but on lifestyle decisions, like binge drinking.
The irony of myopia
In this novel, there is a kind of myopia that plagues the father. He can't see the moon in the sky, but he also can't see his family for who they really are. This is because he has participated so regularly and frequently in certain moods, that he doesn't even really know which set of assumptions is true: the agony of sobriety or the indulgence of alcohol (alcoholism and depression mix badly in this way). The true cost of his alcoholism is his vision.
The irony of nature
On another note, Ondaatje's prose focuses much of its attention on the beautiful balance between human civilization and the unimaginable beauty of verdant jungles, like in East Asia, for instance. The irony of nature is that it is ordinary, primary, essential, but up close, it is mysterious and poignant. Why should something so ordinary give such intense inspiration to an artist like Matisse? Because the inner workings of nature are not as obvious as they might seem to be.
