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[Harry Potter] What counts as dark magic, or unforgivable curses?

If I use a stunning spell to knock someone into the water (nd I'm intending for them to die), does that count as dark magic?

What if I use a memory charm to make someone forget their family?
gpt
The "*Unforgivable Curses*" are three specific spells defined by law as the most heinous offenses that one wizard can commit against another. 

1) The *Imperius Curse*- Robs a victim of their free will, which is the absolute core of human rights and the human condition itself. 

Rowling does a good job of tastefully depicting the horrors of it (although Harry himself uses it later in the books without consequences), but if you really want to read an absolutely gut-wrenching portrayal of how fucked up something like that is, there's a scene in the webseries *Worm* where the character Regent uses his powers (which have a similar effect on people) against Shadow Stalker. It's an undeniably appalling thing to do to another human being and absolutely justifies a life sentence in Azkaban. 

2) The *Cruciatus Curse*- Inflicts unbearable agony on the victim for the purpose of torture. This is pretty much a no-brainer. Torturing people is wrong, full stop, end of story. 

With the *Cruciatus Curse*, there isn't even any plausible deniability because a quick examination of the caster's wand will show that they cast a spell which was created *specifically for the purpose of torturing people*. You'd think if a wizard actually wanted to torture someone and get away with it, they'd use *Aguamenti* to waterboard the person, Guantanamo Bay style. No physical evidence left on the victim, and if your wand is examined, how can the prosecution prove that you used it for torture instead of *literally anything else*? 

3) *Avada Kedavra*- Kills people without causing any detectable physical damage to their body. This is also a no-brainer, but only in the specific context of the Wizarding World. 

In the real world, we allow people to own guns (which are essentially metal wands that can ONLY cast "*Avada Kedavra*") because they are the most effective means of defending an individual's life against an aggressor intent on taking it from them. Less-lethal (no weapon is "non-lethal") weapons don't always work, and an individual doesn't always have one near at hand to even make the attempt. If it's down to "him or you", the law allows you to choose "him".  

However, any wizard in the Harry Potter universe can simply cast a Stunning spell to quickly and easily incapacitate their attacker without killing them. There is therefore no possible justification for using Avada Kedavra against another human being. 

So those are the official "*Unforgiveable Curses*". That gives us a baseline idea for what "Dark Magic" is. It seems to be spells that are specifically designed and intended to cause some sort of harm to another person and don't have any other non-harmful use.

The purpose of a *Stunning* spell is to temporarily incapacitate a person without permanently harming them. If you used it to knock someone into the water with the intent that they drown because they are Stunned, that is not an issue with the spell itself but rather the circumstances under which you chose to use it. If you had stunned your victim on a grassy field, they would still be alive. The water was the cause of death, not the spell. 

The purpose of a *Memory Charm* is to uphold the masquerade by erasing the memories of Muggles who have stumbled upon the knowledge that the Wizarding World exists. It was created to protect wizards by safeguarding the knowledge that they exist at all. If you use it to make someone forget their family, that again is not an issue with the spell itself, but the circumstances under which you chose to use it. 

However, the *Sectumsempra* spell is "Dark Magic" because it was specifically created to harm other people. In the Half-Blood Prince's potions book, the note which accompanies it states very clearly that it's a spell "For Enemies". 

So, in sum: "Dark Magic" is any form of magic in which harmful actions are combined with harmful intentions, and which lacks any non-harmful utility.