The Harry Potter series is a classic tale of good vs. evil, ranking up there with things like Star Wars, Lord of the Rings, and The Chronicles of Narnia. But Harry Potter and the Prisoner of Azkaban really starts to complicate ideas of good and evil – they're certainly not black and white. Nope, this book is about the transition to adulthood, and we all know that journey is full of moral ambiguities, confusion, and difficult choices. The details we learn about the Marauders (James, Sirius, Lupin, and Peter) epitomizes this – their actions as Animagi were dangerous and even morally questionable. We have lots of other good vs. evil complications too: Sirius doesn't always act like "an innocent man" (21.76), Pettigrew is a despicable coward but also pitiable, Snape is presented as both a victim and a villain, and even Ron and Hermione's fights boil down to neither being fully right nor fully wrong.
However, the spells that Harry learns throughout the year put him firmly on the side of good and make certain distinctions clear. Harry uses laughter to fight fear, light to fight darkness, and happiness to fight despair. And we're guessing that these are a big hint that Harry will really need those good tools as he moves into a more uncertain, darker future.