Harry almost killed Malfoy in Harry Potter and the Half-Blood Prince, with it. The next year, George lost an ear due to Snape. These facts, and the "For Enemies" note should clinch it.

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    good question, though, what evidence is there that anyone knew about it other than Snape and Harry?
    – NKCampbell
    Commented Oct 4, 2017 at 23:36
  • 50
    What makes a curse unforgivable? If it was merely any spell with the capacity to cause harm, then thats a lot of spells. Just because its not labeled "unforgivable" doesn't mean its not bad, it just mean that using it won't earn you a lifetime sentence in Azkaban.
    – amflare
    Commented Oct 4, 2017 at 23:38
  • 1
    Sure, a lot of spells can cause harm, but Malfoy could have bled to death. Also, Lupin knew about it, since he made a comment on it.
    – user35971
    Commented Oct 5, 2017 at 0:08
  • 6
    @user35971 Lupin knew about it because he went to school with Severus. So it's unsurprising he knew about it. As amflare says it would mean a lot of spells would be declared unforgivable. But would that also include spells that aren't designed to do harm but actually can if used incorrectly? You could also ask if Dolohov's spell (the purple one that he had to cast silently because he was silenced) should be unforgivable but even assuming anyone would have known about it it's the same question for a different spell.
    – Pryftan
    Commented Oct 5, 2017 at 1:08
  • 3
    Why isn't wiretapping a Deadly Sin? Commented Oct 6, 2017 at 23:17

6 Answers 6


It isn't Unforgivable in the way that the Unforgivables are

A popular fan theory is that there is no grey area with Unforgivable curses. They do what they say on the tin and nothing else. Killing curse kills, imperio controls, crucio tortures. The caster also has to fully understand and mean to cause the effect the curse entails too. There's no excuse for fully casting them other than they wanted to kill/control/torture.

This is alluded to in OotP when Bellatrix taunts Harry about his weak/failed Crucio:

Hatred rose in Harry such as he had never known before: he flung himself out from behind the fountain and bellowed, "Crucio!"

Bellatrix screamed: the spell had knocked her off her feet, but she did not writhe and shriek with pain as Neville had – she was already back on her feet, breathless, no longer laughing. [...]

"Never used an Unforgivable Curse before, have you, boy?" she yelled. She had abandoned her baby voice now. "You need to mean them, Potter! You need to really want to cause pain – to enjoy it – righteous anger won't hurt me for long – I'll show you how it is done, shall I? I'll give you a lesson —" (36.30-32) Order of the Phoenix

And again with fake!Moody in the Goblet of Fire where he claims during the Unforgivables class that if the class were to all point their wands at him and say "Avada Kedavra" he wouldn't get much more than a bloody nose - they'd have to mean it for him to die

"Avada Kedavra's a curse that needs a powerful bit of magic behind it — you could all get your wands out and point them at me and say the words, and I doubt I'd get so much as a nosebleed"


Sectumsempra is different:

Harry is able to fully cast Sectumsempra off-hand and in a panic without understanding any of it's effects. Plus the curse is ambiguous as to how much damage it does, and as Snape proves the damage is reversible. This makes it on par with spells like Reducto, Confringo, or Bombarda Maxima. Each of these spells could be used to decimate another wizard, but also could be used to wound instead.

I would imagine in the HP universe there are more than just three curses that you aren't allowed to use too - the Unforgivables are just the worst and so are on another level. Sectumsempra would most likely regarded as Dark/illegal/restricted, along with other spells such as the organ-expelling/skin-boiling curse etc.

  • 21
    "could be used to decimate another wizard, but also could be used to wound instead." That's a little redundant; decimate means reduce by 10%. Depending on the 10% removed, a wizard could probably likely repair/survive that much damage. Magic can regrow limbs, after all.
    – TylerH
    Commented Oct 5, 2017 at 19:06
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    @TylerH, thanks for that lesson. I, and probably Korthalion, always assumed "decimated" meant similar to completely destroyed. Gives new meaning to "it was totally decimated" haha "it was totally reduced in X by 10%" haha. How anti-climatic.
    – coblr
    Commented Oct 5, 2017 at 23:35
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    @TylerH unfortunately for us pedants, English is a living language: decimate. Commented Oct 6, 2017 at 1:32
  • 10
    I stand by decimate. If you aren't forcing your cohort to kill one in 10, it wasn't a decimation. :) Commented Oct 6, 2017 at 12:03
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    The "decimate" meaning issue can be avoided by using "devastate" or "annihilate". However, even then the connotations of "to decimate" and "to devastate" are to affect a group or region, rather than an individual.
    – outis
    Commented Oct 6, 2017 at 19:50

Not many people knew Sectumsempra - they'd need to know it exists to ban it.

Severus Snape invented Sectumsempra while at Hogwarts, and wrote it down in his Potions book. He doesn't seem to have told many people about it, it's possible he didn't tell anyone at all.

“Harry was about to put his book away again when he noticed the corner of a page folded down; turning to it, he saw the Sectumsempra spell, captioned ‘For Enemies’, that he had marked a few weeks previously.” - Harry Potter and the Half-Blood Prince, Chapter 24 (Sectumsempra)

His book was hidden away until Harry found it, and Harry didn't tell the rest of the wizarding world about it either. Severus himself was seen using Sectumsempra when the Order was moving seven Harrys, and Harry had used it a few times after he found it in Snape's old book. Lupin knows of it, since he described it as one of Snape's specialties.

However, they are probably some of the only people who know it - it isn't widely known like the three Unforgivable Curses. No one else, either in the Death Eaters or the Order of the Phoenix, is ever said to use it. It's likely that the Ministry didn't even know of it. Therefore, the Ministry wouldn't have even been able to make the decision to classify it as an Unforgivable Curse, since they would likely not have even known it existed.

If the Ministry knew about it, would it be classified as Unforgivable?

The reason it wasn't classified as an Unforgivable Curse is because the Ministry wouldn't have known about it - they would be unable to make any decision on something they don't know exists. That, by itself, doesn't say whether the Ministry would classify it as one if they knew about it.

Not all potentially harmful spells are classified as Unforgivable Curses.

It's nowhere near guaranteed, though, that if the Ministry knew about Sectumsempra, that they'd classify it as an Unforgivable Curse. There are other spells that could clearly do harm. Just to give a few examples - Confringo, Flagrante, and the creation of Fiendfyre are all potentially harmful but not Unforgivable.

It's never mentioned why those three curses are classified as Unforgivable and others aren't, but it seems likely that it's because there are little to no uses for them that aren't evil. The punishment for using an Unforgivable Curse is a lifetime sentence in Azkaban, so only the worst curses, that are highly unlikely to ever have a non-Dark use, would be made Unforgivable.

“Now … those three curses – Avada Kedavra, Imperius and Cruciatus – are known as the Unforgivable Curses. The use of any one of them on a fellow human being is enough to earn a life sentence in Azkaban.” - Harry Potter and the Goblet of Fire, Chapter 14 (The Unforgivable Curses)

Now, would Sectumsempra fit the criteria for being made an Unforgivable Curse?

Probably not - it cuts through things like a sword. It can be used for anything a sword, knife or other cutting tool can be used for. While using it on people might be considered Unforgivable, the spell itself is simply the act of cutting. There are many things a wizard might reasonably want to cut with no malicious intent; vegetables, rope, cloth, building materials. Because of this, it seems unlikely that even if the Ministry had known about it, it would be classified as an Unforgivable Curse.

In addition, there is a countercurse for Sectumsempra.

“Pushing Harry roughly aside, he knelt over Malfoy, drew his wand and traced it over the deep wounds Harry’s curse had made, muttering an incantation that sounded almost like song. The flow of blood seemed to ease; Snape wiped the residue from Malfoy’s face and repeated his spell. Now the wounds seemed to be knitting. - Harry Potter and the Half-Blood Prince, Chapter 24 (Sectumsempra)

While the wounds from Sectumsempra can't be healed by simple healing spells, they can in fact be healed by the countercurse.

So - Sectumsempra likely wouldn't be made Unforgivable if the Ministry knew it.

  • The fact that the cut is a cursed one(which cannot be reversed by, say, Reparo or Episkey) should make a strong case.
    – cst1992
    Commented Oct 5, 2017 at 18:20
  • 1
    @cst1992 Yes, if Sectumsempra is used to cut a person. However, although it's only shown being used on people, it's never stated that's it's only use. It might have other uses. If it was used to cut a tarp, for example, or anything that doesn't need to be healed, it wouldn't matter.
    – Obsidia
    Commented Oct 5, 2017 at 18:49
  • 1
    My tarpaulin friend is very offended that you think he doesn't need to be healed when cut. -1 (just kidding, I upvoted) Commented Oct 5, 2017 at 21:59
  • @cairdcoinheringaahing Well, once someone knows the countercurse, like Snape used on Draco, your tarpaulin friend will be good as new! :)
    – Obsidia
    Commented Oct 5, 2017 at 22:52
  • If the M.O.M didn't know about it, that would mean that Snape never used it in the first war.
    – user35971
    Commented Nov 8, 2017 at 3:56

Since only Snape and Harry ever cast it, the Ministry doesn't really need to be concerned

Severus Snape invented Sectumsempra. When Harry tried to cast it on Snape, he said:

"You dare use my own spells against me, Potter? It was I who invented them ~ I, the Half-Blood Prince!"

—Harry Potter and the Half Blood Prince

Let's assume that Snape is telling the truth on this and that he did indeed create it. The only two people we see cast it are him (Lupin said that Snape was the one who cut off George Weasley's ear at the Battle of Hogwarts) and Harry (who vows never to use it again).

Snape is at this point is a known Death Eater and there isn't much point in criminalizing a spell that only he is casting. And the Ministry seems unaware that Harry committed it.

But if the Ministry starts getting hundreds of reports that non-Deatheaters were casting it, they might have decided to make it an Unforgivable Curse.

Sectumsempra could have forgivable uses

In Why isn't the Memory Charm (Obliviate) an Unforgivable Curse?, the highest answers note that despite a potential for horrific abuse, the Ministry uses the Memory Charm regularly for accepted, legitimate uses. However, the Unforgivable Curses like Cruciatus are assumed to not have legitimate uses.

It's possible that there could be a case where "slashing like an invisible sword" could be useful. Perhaps it could be used for cutting down trees, or for medical amputation, or for slaughtering farm animals. If any of these are seen as reasonable uses for the curse, then there are circumstances where casting Sectumsempra may be forgivable.

Curses just as bad aren't Unforgivable

There are plenty of other spells that are arguably just as dangerous or undesirable (including the Blasting Curse and the Lycamoia Curse).

Heck, if we're following the movies, the Blow People Up Into a Million Pieces Curse is arguably worse than Avada Kedavra, but it's perfectly okay for Molly Weasley to do it.

  • 1
    Lupin knows about it; and I thought Harry mentions it to Ron and Hermione and maybe Ginny (? unsure on the last one). I suspect that James (want to say it was even used on James but not sure here) as well as Sirius and Peter knew about it; Lupin does say in DH that it was known at Hogwarts in their time.
    – Pryftan
    Commented Oct 5, 2017 at 1:11
  • And even if he doesn't mention it to Ginny Lupin mentions it at the Burrow after the Battle [of the] Seven Potters. So all the others would have known about it too.
    – Pryftan
    Commented Oct 5, 2017 at 1:16
  • @Pryftan Fair point, I've changed my answer to say that only Snape and Harry have cast it, and there's not much point in criminalizing it if it's just them. Commented Oct 5, 2017 at 1:33
  • 1
    That's probably quite true yes. Even then though I don't think it'd be declared unforgivable. There are many other curses that can kill and many spells more generally that might not directly cause harm but can if used incorrectly or maliciously. Intent is the key I think as Bellatrix pointed out in her answer.
    – Pryftan
    Commented Oct 5, 2017 at 1:43
  • 1
    @Bellatrix I personally think that Molly Weasley should get a one-way trip to Azkaban for killing you like that! Commented Oct 5, 2017 at 20:16

Because at most two or three people seemed to know about it.

The spell literally only appears on people tightly related to Snape. The only reason Harry knew the spell is because he ended up with Snape's old textbook with the notes in it.

It's not like the Ministry of Magic has enough time or competency to run down every possible combination of dark magic, and draft particular laws against each. They'd have to be adept at researching and doing dark magic and find unknown spells to begin with, which is ground very few are willing to tread.

The Unforgivable Curse laws covered the three most well known spells, and with those three the most common goals of those following the dark arts - domination, control, and death. Anything else they probably have a more generic law for. "Magic with intent to murder" ought to cover it, which would cover anything from Sectumsempra to levitating an anvil.

  • Seems like a job for the Aurors
    – Mikasa
    Commented Oct 6, 2017 at 14:30
  • 2
    @MikasaPinata - it probably is their job to research dark magic. But what would practical wizards on the front lines then do with that? Figure out a defense against it, or scribble down some law on paper about how it's bad? Which then, coincidentally, lets every two-bit magical know exactly what they found?
    – Radhil
    Commented Oct 6, 2017 at 14:56

What is an unforgivable curse?

From what we know of them, the unforgivable curses all need to meet all the following conditions:

  • They require full intent
  • They are meant solely to cause harm
  • There is no countercurse
  • The intended harm cannot be reversed (Death, pain, control/action by proxy)
  • They are primeval spells (meaning they were invented before the formalization of magic, spells and the civilised magical world).

As can quickly be seen, sectumsempra fails at least 3 of these. It is not an unforgivable curse.

  • 1
    FYI, your last sentence should be your first. Also, I was unaware that they were primeval spells. What's the source on this?
    – amflare
    Commented Oct 5, 2017 at 14:05

Its cause the guy who made the spell only knew about it, yes professor snape is the half-blood prince.

Also only snape had a spell to undo it, Salazar Slytherin proberly also had spells to undo the unforgiveable curses, but he took it too the grave, like snape would with his spells.. Salazar Slytherins spells wasent unforgiveable back in the days, it wasent until Ulick Gamp was elected minister of magic, that he made the spells unforgiveable. thats almost a 800 years they werent unforgiveable.. salazar was born around 900.. Ulick Gamp was minister in 1707

My thoughts: I would reckon they eventually could become unforgiveable, if the counter spells was not to be recovered, so eventually the use of them would be considered too dangerous and unforgiveable. But lets say we lived in a world where we practised these spells and the counter spells from the book of the half-blood prince, then they would be considerable less dangerous, cause people would know what to do, to save them from it. So for a spell to become unforgiveable have more factors than being a killing curse like avada kadavra. E.g. Imperio takes away your free will, and do the casters bidding, untill the very end, and you wouldnt know the difference from the guys who went willingly or was under the spell. Crucio tortures your living soul, and it wont go away. All these spells need the one factor, of having a counter spell. But they dont.

  • 2
    Hi, welcome to SF&F. Do you have any evidence that it is the existence/non-existence of counterspells that determine if a dangerous spell is Unforgiveable, as opposed to the textual evidence (see the first answer) that intent matters?
    – DavidW
    Commented Feb 14, 2023 at 15:55

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