The Harry Potter saga made some changes to the books and ended up creating an underage magic plot hole. Here’s what happened.
Although the Harry Potter movie saga was quite loyal to the books, it made some changes to better fit the format, and while most worked well, there are others that ended up creating plot holes. Such is the case of the Trace, which was inconsistent throughout the movie series. In 1997, readers were introduced to the Wizarding World in J.K. Rowling’s debut novel Harry Potter and the Philosopher’s Stone, the first entry in what would become a series of seven novels. The books told the story of “the boy who lived” and Lord Voldemort, the darkest wizard of all who had some dangerous plans.
The Harry Potter novels were a big hit, and it wasn’t long until they made the jump to the big screen. The Harry Potter saga was released between 2001 and 2011, with the final book, Harry Potter and the Deathly Hallows, divided into two movies. The saga expanded the fanbase of the novels and made the Wizarding World, its events, characters, objects, and more part of pop culture, but the movies also made some big changes to the books. A universe as rich as that of Harry Potter (understandably) couldn’t fit in eight movies, so some characters had to be left out, events were left unexplained, and some things were inconsistent, thus creating plot holes, which is what happened with the use of magic outside of Hogwarts.
It was established since Harry Potter and the Philosopher’s Stone that wizards under 17 years old are not allowed to perform magic outside their schools, in this case, Hogwarts. In order to ensure that this rule wasn’t broken and that those who did were punished, the Ministry of Magic tracked the magical activity of “underage” wizards through a charm known as the Trace. Whenever a young wizard used magic outside their school, the Improper Use of Magic Office within the Ministry was alerted through the Trace, letting them know the spell that was used, the location of the caster, and the time it was cast. The Trace was broken automatically on a wizard or witch’s 17th birthday, after which they could use magic outside their schools.
Now, in the movies, Harry Potter used magic outside Hogwarts, and even worse, in the Muggle world, a couple of times without any repercussions. The one that is still questioned by fans is at the beginning of Harry Potter and the Prisoner of Azkaban, when Harry is using Lumos Maxima while studying in his room, something that went unnoticed by the Ministry. This spell and scene are exclusive to the movie, as in the novel, Harry is writing an essay with the help of a regular flashlight. Another example of the Trace being inconsistent in the Harry Potter movies can be found in the first movie, when Hermione uses Oculus Reparo to fix Harry’s glasses aboard the Hogwarts Express and again in Harry Potter and the Chamber of Secrets but now in Diagon Alley. It’s possible that, at least in the movies, the Trace overlooked harmless and simple spells like those or that the Hogwarts Express is considered an extension of Hogwarts, though that doesn’t explain the unpunished use of Lumos and Oculus Reparo in Diagon Alley.
There’s also that one incident where Harry accidentally inflated Aunt Marge, with then Minister of Magic Cornelius Fudge telling him that they “don’t send people to Azkaban for blowing up their aunts”. It’s possible that the Trace (in the movies) was there just to keep control of the activity of young wizards, and not every use of magic granted some sort of punishment – but this still doesn’t fit with Harry receiving a warning for everything Dobby did at his home in Chamber of Secrets. The Harry Potter movies didn’t pay attention to the Trace and how it works, making way for a plot hole and a lot of confusion that Rowling hasn’t clarified yet.