In Harry Potter and the Sorcerer's Stone, all of Harry's professors create an obstacle. Noticeably missing are obstacles related to courses that Harry isn't currently studying, such as Divination, Muggle Studies, Arithmancy, or Ancient Runes.

Is there an in-universe reason why there were no obstacles created by those professors? (Out-of-universe, the answer seems to be obvious.)

Inspired by this post on Reddit.

  • 18
    Three is a magic number :) One could argue that Dumbledore only revealed the existence of the Stone to three teachers, and that three was considered sufficient (law of diminishing returns). That doesn't explain why Dumbledore didn't trust more teachers, or a different set of teachers, but one should only look for so much internal logic in a book the revolves so strongly around the protagonist and what is required for the predetermined ending.
    – chepner
    Commented Jul 19, 2020 at 14:49
  • 10
    Consider that you have a new cell-phone monitoring system, rumored to exist, but not widely believed to exist and certainly not confirmed to exist. Consider that having access to it could give the possessor very considerable power. You need help in protecting it, but, the more people who know it exists, the more likely word is to get out and the more likely others are going to try to gain access to it. You tell the absolute minimum number of people necessary about it when enlisting their help to protect it.
    – FreeMan
    Commented Jul 19, 2020 at 15:16
  • 14
    @Chepner three teachers ? There were Mcgonagall, Sprout,Quirrel,Snape Commented Jul 19, 2020 at 16:22
  • 11
    @TheMadHatter And Flitwick and Hagrid.
    – Showsni
    Commented Jul 19, 2020 at 20:41
  • 6
    @FreeMan right, this is a major way that Classified information is protected in our own world. If you don't need to know it, nobody tells you, even if you have the "correct" clearance for it. Commented Jul 20, 2020 at 10:39

6 Answers 6


Their assistance would not be useful.

What would Trelawney be able to do? She only has prophetic powers when she has a vision, which is not under her control. What would Professor Sinistra, the Astronomy teacher, be able to do? So far as I can tell, astronomy in the magical world is nothing more than mundane astronomy. I think Muggle Studies would be fairly useless, and both Arithmancy and Ancient Runes seem to be helpful for other kinds of magic, but less so themselves.

In other words, the other professors teach theoretical or abstract subjects, which is why their courses are more advanced. Whereas the core teachers give practical courses, and so their knowledge is more useful for actually creating obstacles.

  • 71
    The Muggle Studies could have been the most useful, because of the Muggles having figured out that a good security system is based on discriminating unauthorized people from authorized ones, and not one which lets anyone through who can solve some logic puzzles (some of which even have written instructions laying nearby!).
    – vsz
    Commented Jul 20, 2020 at 7:45
  • 19
    @nick012000 : I wasn't talking about muggle devices, just about the idea of selecting between authorized and unauthorized personnel, instead of selecting between those who can or cannot solve a riddle. Even with the same setup, why include the correct key among the flying ones (especially as it even looks different than the decoys), instead of giving copies to authorized people only? And why include written hints to the potions puzzle instead of just keeping the number of the correct potion a secret? And why not include spells which silently alert the authorities?
    – vsz
    Commented Jul 20, 2020 at 9:46
  • 43
    "I thought we were supposed to be keeping the Stone safe. Of course the riddle was a lie and all the potions were debilitating poisons! If you wanted challenges passable by first-year students, you should have said so in the planning session."
    – notovny
    Commented Jul 20, 2020 at 11:13
  • 13
    @notovny : This is handled nicely in HPMOR, where the only real security measure is the mirror itself, which is a trap set up by Dumbledore, who is alerted as soon as someone appears - and is trapped - in front of the mirror (the original book doesn't have this feature). The other tasks have their only goal of slowing down the intruder, and are safe for first-year students because Dumbledore suspected Voldemort will try to trick some students to fetch the Stone for him.
    – vsz
    Commented Jul 20, 2020 at 12:35
  • 9
    @vsz, my theory is that we're looking at a rule of magic: a properly formed magical challenge cannot be bypassed by any means, but in order to be properly formed, they have to be fair, it has to be possible to win, at least nominally. That would mean that if you didn't (for example) leave the key in the third chamber, an intruder would be free to use Alohomora on the door, or stronger magic to break it down, or other magic to bypass the challenges entirely. Compare Riddle's defenses protecting the locket in the sixth book. Commented Jul 20, 2020 at 18:40

From Chapter Fourteen of Philosopher's Stone:

“Oh, come on, Hagrid, you might not want to tell us, but you do know, you know everything that goes on round here,” said Hermione in a warm, flattering voice. Hagrid’s beard twitched and they could tell he was smiling. “We only wondered who had done the guarding, really.” Hermione went on. “We wondered who Dumbledore had trusted enough to help him, apart from you.”

While Hermione might be totally making this up, it is possible that she has correctly identified the point, namely, that Dumbledore trusts certain people. According to this we can surmise that those who helped protect the stone were the teachers that Dumbledore particularly trusted.

  • 11
    Such as Quirrell!?
    – TheAsh
    Commented Jul 19, 2020 at 15:44
  • 5
    We know Dumbledore didn't trust Quirrell: He tells Snape to "keep on eye on him"
    – MBEllis
    Commented Jul 19, 2020 at 19:53
  • 5
    @TheAsh There's no point baiting a trap unless your intended victim knows where the bait is. Commented Jul 20, 2020 at 12:33
  • I assume he trusted all of his staff, Quirrell was probably trustworthy prior to being possessed.
    – rtaft
    Commented Jul 21, 2020 at 13:20

Possibly limited to heads of houses and other important persons rather than all staff.

Fluffy - Hagrid (trusted person)

Plants - Professor Sprout (Herbology), Head of Hufflepuff

Flying Keys - Professor Flitwick (Charms), Head of Ravenclaw

Chess - Professor McGonagall (Transfiguration), Head of Gryffindor & Deputy Headmistress

Potions - Professor Snape (Potions), Head of Slytherin

Mirror - Professor Dumbledore, Headmaster

  • 8
    Only falls down in that Quirrell was also included, where he contributed a troll
    – Joe
    Commented Jul 20, 2020 at 8:44
  • 7
    @Joe If Dumbledore suspected him from the start, then he may have been included as bait and a distraction (i.e. he spent almost the whole school year hounding the teachers to discover their protections, instead of just sneakily inspecting the traps with the excuse of checking up on the Troll - at least, after his first attempt on Halloween failed.) Commented Jul 20, 2020 at 10:38
  • 5
    @Joe Quirrell was the defense against dark arts instructor which is why he might have been included.
    – Joe W
    Commented Jul 20, 2020 at 16:02
  • 5
    @JoeW: Indeed, the whole thing was basically a practical exercise in DADA techniques (they're trying to keep dark wizards away from the Stone), so you can't reasonably exclude the DADA professor without raising a whole lot of uncomfortable questions about why. Dumbledore was obviously keeping a lot of people in the dark about his suspicions w.r.t. Quirrell, and he probably didn't want to go public with them at that point in the story.
    – Kevin
    Commented Jul 20, 2020 at 18:16
  • @Chronocidal He may not have suspected Quirrell at first, he was a trusted teacher prior to being possessed. Letting a troll loose in the castle was a dead giveaway that he was up to something.
    – rtaft
    Commented Jul 21, 2020 at 13:13

Because had any more professors been involved, there would have been more than seven obstacles. This is Harry Potter. Everything is about the number seven.

I'm not sure if this is what you refer to as the obvious out of universe answer. But even in-universe, characters know the power of seven, for example the deliberate number of Horcruxes, or the ways of scoring in Quiddich.

Another answer is that Dumbledore wanted obstacles that would stop Voldemort (if he had returned) but would not stop Harry (and his friends). Or, as the inspiration for the question says, "A first year should technically be able to get through with the help of some friends." By restricting the professors to those that knew Harry personally, he could make sure the challenges were things that Harry, specifically, could overcome.

  • 4
    Re: "I'm not sure if this is what you refer to as the obvious out of universe answer": I think the out-of-universe answer that the OP alludes to is that Rowling either hadn't yet come up with those professors, or didn't want to introduce them just for this one thing.
    – ruakh
    Commented Jul 20, 2020 at 5:03
  • Are you counting the locked door as an obstacle? Commented Jul 20, 2020 at 7:20
  • 2
    @HarryJohnston; No I don't believe so; Fluffy, Devil's Snare, Keys, Troll, Chess, Potions, Mirror.
    – Jontia
    Commented Jul 20, 2020 at 8:28
  • 1
    @ruakh correct.
    – TheAsh
    Commented Jul 20, 2020 at 16:39
  • 1
    ... this reinforces your point, I think. It strongly suggests that the author may have deliberately arranged things so that Dumbledore created exactly seven challenges and Harry faced exactly seven challenges, even though there was one extra at the end. +1. Commented Jul 20, 2020 at 18:30

It's possible that the traps were meant to serve multiple uses...

  1. Allow Dumbledore through, without too much hassle.

  2. Slow-down - rather than stop - someone trying to get the stone, so that Dumbledore could be notified (wards) and had time to intervene.

  3. Serve as test for Harry Potter (whom Dumbledore knew eventually would have to be the one to stop Voldemort) and his friends. If so, it makes very much sense to only use the teachers teaching 1st year subjects. (In addition, Hagrid conveniently gave Harry a flute for Christmas to put Fluffy to sleep.)

  4. Make sure no one teacher could easily disable all traps using their own expertise.

  5. Test the teachers' loyalty, by seeing how difficult their traps were (eg. Quirrel's troll).


If Dumbledore just wanted to keep the stone safe, why use a simple locking-charm that several students (including 1st year Hermione) could bypass?

If Dumbledore wanted to keep the stone safe, why not bury it under the stone-floor of his personal quarters (accessed through his office, protected by a gargoyle) and use many layers of wards?

Why tell all the students at the welcome-feast, in a way that almost guaranteed some students would try to find-out what was hidden?

The only real safety-measure was the mirror, as someone who wanted to actually use the stone, would spend hours trying to get to it... assuming they didn't also succumb to the magic of the mirror, and "wasted away in front of it".


So I would think everything but the mirror were just slow-down an intruder, and to test Harry and his friends. If Dumbledore wasn't away, I'm sure he'd observe Harry's journey through the traps - maybe he did.


While I think that the other answers provide quite reasonable answers, I think it's also important to recognize the rather special relationship Harry and Dumbledore have throughout the series, as well as the connection between Harry and Voldemort. Dumbledore makes a habit of spinning lots of plates at once, making things seem disconnected, until (unsurprisingly given the name of the series) it turns out to all be about Harry - Snape's revelation in book seven is the epitome of this.

All that is to say that:

Voldemort will make it through any security system, so Harry needs to be able to as well.

Harry, at this point, is the one thing that can stop Voldemort in the end. Dumbledore knows this, and intends for Harry to get involved in order to stop it. Dumbledore can't do it himself because:

  1. He doesn't want to show his hand. He's still amassing power against Voldemort, and doesn't want him to come out of hiding too early.

  2. He needs Harry to start believing in himself and his ability to fight against Voldemort, if he wants Harry to be an effective fighter.

Furthermore, Dumbledore doesn't want it to be someone else besides Harry, because he knows that Harry is still protected by his mother, and will never just give the stone away.

It's pretty clear that Harry was meant to get through these challenges - they're basically tailor made for him and his friends. The only reasonable explanaition for such a personalized set of tasks is that they were meant to be that way.

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