Nick Hornby raises several themes in the novel, and the three principal ones are as follows:
The novel is concerned with the way that people are isolated from others in different ways; either by their own choice or because of their circumstances. The two main characters, Marcus and Will, are both
loners at the start, but for differing reasons, and as the novel progresses, we see how they are gradually absorbed into a wide net of people, which makes them much happier in the long run.
The theme of adulthood and growing up is a theme which runs through the novel. Will actually is an adult who has never wished to accept the fact. He tries desperately to be cool and trendy, not realising that he is pitied by other people of his own age for not growing up. Marcus actually is a child, but he has so many worries that he feels weighed down by them, instead of being carefree as a child should be.
The theme of depression/mental illness is one that concerns the author, Nick Hornby, very much. Fiona, Marcus’ mother, suffers from depression and attempts suicide at one point in the novel. This naturally affects not just Fiona, but Marcus as well, and even has wider repercussions among their friends.