How come the Ministry of Magic's detection of magic usage is inconsistent?

Question

In the Harry Potter and the Philosopher's Stone Hagrid scares the Dursleys by using magic to put a tail on Dudley, apparently without any consequences from the MoM. But in Order Of the Phoenix, Harry barely makes it home after saving Dudley from the Dementor attack when the MoM hits him with a code violation.

I understand that the exact clause of the violation in OP is underage magic use, but wouldn't Hagrid be breaking the Statute of Secrecy by using magic in front of a most-definitely-Muggle such as Vernon Dursley?

Answer 1

From an out of universe perspective, it's inconsistent because it's used to advance the plot in certain situations, but would be an unnecessary distraction in others.

However, from an in-universe perspective, we can address the two specific situations you mentioned.

Dudley's tail in Philosopher's Stone

The Ministry finds out about underage magic using The Trace, which detects magic by - or in the vicinity of - anybody under the age of seventeen. This would definitely apply to Harry who had just turned eleven.

However, there are two likely explanations:

1. The Ministry ignores any magic performed in the vicinity of underage wizards who have not yet started attending Hogwarts (or another magical school), assuming that it's more than likely unintentional magic performed by an untrained wizard.

2. Dumbledore informed the Ministry that he was sending somebody in person to fetch Harry as he hadn't received his Hogwarts admission letter, and that there would likely be some magic performed near to him as part of that process. (It seems unlikely that he would have told them who he was sending, as Hagrid wasn't allowed to perform magic at that time.) Therefore they would ignore any magic performed near him.

As an aside, as Harry's guardians, the Dursleys were already aware of the existence of the Wizarding World. Therefore it should not be possible to breach the International Statute of Secrecy by performing magic in front of them.

Harry's Patronus charm in Order of the Phoenix

Harry had attended Hogwarts for four years, and was - on the whole (no pointing out Aunt Marge, please!) - capable of controlling himself and not performing any magic unintentionally. Therefore any magic that was performed in his vicinity would be assumed to have been performed intentionally.

It's also worth remembering that Harry had told everybody that Voldemort had returned at the end of the previous school year, and that this was something that the Ministry did not want to admit. They had therefore engaged in a propaganda campaign to discredit Harry as much as possible. His conviction for performing underage magic was simply one more part of their attempts to discredit him.

Answer 2

The Trace is only enforced for students attending Hogwarts.

Harry also didn't get into trouble for any of his accidental magic before he starts attending Hogwarts, like his hair magically growing back, or releasing the snake from its habitat. He's only restricted from using magic outside Hogwarts and in front of Muggles once he finds out from Hagrid that he's a wizard. Hagrid scares the Dursleys by using magic before he tells Harry he's a wizard, because that's how he gets the Dursleys to let him tell Harry. So at that time, the Trace wouldn't be actively enforced on Harry since he still wouldn't know yet.

In addition, Harry conjured his Patronus on a Muggle street, risking being seen.

The incident Harry was in trouble for was him casting a Patronus Charm in a Muggle-inhabited area as well as in view of a Muggle.

“We have received intelligence that you performed the Patronus Charm at twenty-three minutes past nine this evening in a Muggle inhabited area and in the presence of a Muggle.” - Harry Potter and the Order of the Phoenix, Chapter 2 (A Peck of Owls)

Hagrid, however, scared the Dursleys with magic in a secluded hut, where no one but them could see.

Answer 3

The way that the Ministry detects underage magic is with The Trace, but it only applies to people under the age of 17. Hagrid is over the age of 17, so he doesn't have the Trace on him. Therefore the only way the Ministry would know is if someone reported him, which the Dursleys are unlikely to.

"The Trace, the Trace!" said Mad-Eye impatiently. "The charm that detects magical activity around under-seventeens, the way the Ministry finds out about underage magic! If you, or anyone around you, casts a spell to get you out of here, Thicknesse is going to know about it, and so will the Death Eaters.

"We can't wait for the Trace to break, because the moment you turn seventeen you'll lose all the protection your mother gave you. ..."

The Deathly Hallows, Chapter 4

As for when Hagrid was with Harry in Philosopher's Stone, he was given special dispensation to use magic to retrieve Harry Potter, but was barred from doing so once he had him. So the time when he's retrieving him, the Trace was expected to be activated a few times as necessary:

"How did you get here?" Harry asked, looking around for another boat.

"Flew," said Hagrid.

"Flew?"

"Yeah --- but we'll go back in this. Not s'pposed ter use magic now I've got yeh."

Philospher's Stone, Chapter 5 (Bold mine)

If he's not supposed to use magic now, he was allowed to before. Since he continues using it, only stipulating that Harry not tell, he must expect that any further triggers of the Trace will be covered under Dumbledore's permission or, as BMWurm suggests in the comments, it may be assumed that it is simple uncontrollable magic. They don't go after Harry earlier when he accidentally makes the glass disappear in the snake enclosure.

Answer 4

In addition to Anthonys answer, yep the Ministry tend to turn a blind eye to magic performed by or around those under the age of 11, without a wand in a non wizarding household. As Harry didn't have a wand (and nor did Hagrid technically), i'm sure they would have let him off the hook. Bear in mind he had already done magic before (vanishing glass and apparating to the school roof from Philosophers Stone).

Furthermore, Snape mentions it to Lily near the end of the book 7.

"...and the Ministry can punish you if you do magic outside school, you get letters." "But I have done magic outside school!" "We’re all right. We haven’t got wands yet. They let you off when you’re a kid and you can’t help it. But once you’re eleven," he nodded importantly, "and they start training you, then you’ve got to go careful." - Snape and Lily, The Princes Tale, Deathly Hallows

A young Snape probably would have been quite well informed as well...

“Snape knew more curses when he arrived at school than half the kids in the seventh year and he was part of a gang of Slytherins who nearly all turned out to be Death Eaters.” - Sirius Black, Goblet of Fire

Answer 5

The statute of secrecy is moot in this case. To Vernon Dursley, the secret has been no secret for at least since Harry was dropped on their doorstep. Even if Petunia hadn't told Vernon about her sister being a witch before that (which she definitely did), the letter from Dumbledore necessarily had to introduce Vernon to the magical world:

'It's the best place for him,' said Dumbledore firmly. 'His aunt and uncle will be able to explain everything to him when he's older. I've written them a letter.'

(see the excerpt from The Philosophers Stone)

In addition, the behaviour of Vernon and Petunia towards Harry described in the second chapter makes it obvious that they know about magic and Harry being a wizard. They scold him for the tiniest extraordinary thing happening because they fear it might be a sign of Harrys magic. Even when Harry tells about a weird dream he had, Vernon overreacts and reprimands Harry.

And if Vernon would have harbored any hopeful doubt, the unsuccessful attempts to deliver the invitation to Hogwarts would have left him none at all. So Hagrid would be tasked to break the statute of secrecy more than it already has been.

Answer 6

In-universe Harry still hasn't gone to Hogwarts, and is unaware of the illegality of magic, and since he's untrained, I believe that the ministry would have interpreted it as accidental magic. I don't think the ministry would have much success trying to punish kids under Hogwarts age for magic because it's still uncontrollable for them--they haven't been trained. Since Hagrid was in the same room as Harry when he hexed Dudley, it would have been registered as happening around an underage Harry, who wouldn't have been punished. However, once Harry started going to school, and received the notes telling him about the illegality of magic over the holidays this protection wasn't valid any more (hence his being blamed for Dobby's hover charm over the holiday between first and second year). The same could be said for Tom Riddle's curse of his uncle Morphin Gaunt--the magic was performed in a magical house, and while Tom was underage, the ministry had no idea that he was there, so the magic was interpreted to have been Morphin's alone.

"'you are quite right--they can detect magic, but not the perpetrator: you will remember that you were blamed by the Ministry for the Hover Charm that wa,s in fact, cast by--' 'Dobby,' Hary growled...'So if you're under age and you do magic inside an adult witch or wizard's house, the Ministry won't know?' 'They will certainly be unable to tell who performed the magic,' said Dumbledore...'they rely on witch and wizard parents to enforce their offspring's obedience while within their walls.'"
_{Half-Blood Prince, page 344}