Author: Maryh
What makes magic Dark?
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The first definition that comes to mind is magic that causes harm to others. However, virtually every hex and jinx falls into that category, and nobody has ever said that Fred and George, for example, are involved in the Dark Arts.
Is the type of harm done by the magic what makes it dark? But dark magic need not cause any physical, emotional or mental harm, since the Imperius curse is Dark, and does not do this. On the other hand, magic may cause all three types of harm without being considered Dark. A great many jinxes cause physical harm, a love potion can definitely cause emotional harm, and Obliviate can definitely cause mental harm. While some of these may even be considered dangerous, none are considered Dark.
Is the permanence of the damage caused what makes magic Dark? The effects of every jinx or hex we've encountered so far in canon that isn't considered Dark can be cured. The three unforgivables can cause permanent damage: AK, obviously; cruciatus emotionally and potentially mentally, and Imperius because the target may not be able to undo what they did under its influence. Interestingly, the only exception I can see to this general rule in canon are memory modification charms.
I think we're on the right track. This is related to the other thread that runs through all Dark magic, which is the degree of harm done. Dark magic causes significantly more damage. This is still a subjective measure, but I think it is reasonable for there to be a gray area between Dark magic, and magic which is dangerous but still not considered Dark. So let's say that Dark magic is magic which causes significant and usually irreversible harm to people.
That still doesn't necessarily make it evil, though. A Muggle analogy to the Dark Arts would be the use of deadly force, which most people don't consider evil in the case of self defense, or when used by the police, when necessary, to apprehend dangerous criminals. You might expect Aurors to be authorized to use at least the AK curse as a matter of course when necessary, to apprehend criminals, just like Muggle police officers use guns. And yet, Barty Crouch's decision to allow the use of the Unforgivables appears to have been highly controversial, and there is no implication that if he had just stuck to the AK curse, and not legalized the other two, it would have been more palatable to wizards in general and to Dumbledore in particular.
Is it evil to be a Dark Wizard?
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The comparison of the Dark Arts with the military arts among Muggles looks like a good one at first glance. But the military profession is considered both honorable and necessary in most, although not all, societies that I know of. And yet we have no example in canon of any wizard who actually practices the Dark Arts being considered honorable outside of the circle of Dark Wizards. Not even the Aurors are supposed to use the Dark Arts. Where is the Wizarding World's equivalent of the United State's General Lee during the civil war, or Germany's Field Marshal Rommel during World War II? Why don't wizards practice the Dark Arts in competitions analogous to skeet shooting or archery or jousting?
I think it is because of the very different ways magic works compared to technology. There are two significant differences, which I believe explain why the Dark Arts are tolerated in the Wizarding World, but not accorded the status, outside their own practitioners, that the military arts get in the Muggle world.
Firstly, in the Muggle world, it is possible to practice deadly arts without actually harming anyone. A gun can be pointed at another person, but it can also be pointed at a clay pigeon. An arrow can kill an enemy, or simply hit a target. I cannot see how any dark magic can be practiced without causing harm to another person, or at least an animal.
But secondly, and most importantly, it does not appear to be possible, from canon, to perform Dark Magic without malevolent intent. You cannot kill using the AK unless you can muster sufficient hate. Your cruciatus will not work without the necessary amount of sadism. In the ethical/moral systems I am most conversant with in the Muggle world, use of deadly force is supposed to be used as a last resort and with regret at the necessity to use it. The military leaders and soldiers that we consider most honorable do not kill out of hate, but out of what they perceive as necessity. In the Wizarding world, it is not possible to separate the two.
My conclusion is that the Dark Arts are inherently more evil than the military arts in the Muggle world. So can we say that Dark Wizards are evil, and just tolerated by the Wizarding community because, after all, they still need the capability for self defense? Sort of. But if that were the case, why don't we see a cadre of Dark Wizards fighting Voldemort instead of the Aurors? My conclusion is that any Wizard who uses Dark Magic is playing with something inherently evil, and that anyone who goes so far as to consider them self a Dark Wizard is doing something evil.
What about Snape?
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So where does that leave a wizard like Snape, who loves the Dark Arts, and has always coveted the DADA position?
First of all, Snape has never been called a Dark Wizard in canon. Nor, until the very end of HBP, have we ever seen or even heard of Snape using any of the unforgivable curses, something which cannot be said of Harry himself. In fact, while we are repeatedly told that he KNEW more dark spells than anyone else when he first came to Hogwarts, we are never told of any that he actually USED, apart from sectumsempra, which he appears to have invented himself. (And I was surprised to see sectumsempra, which is no more permanent or damaging than other hexes, called dark while other hexes are not. Was Snape testing the boundaries of the gray area?) The silence on this subject is remarkable, since there are no lack of witnesses in canon who would be pleased to report on Snape's skill with Dark magic. Sirius comes to mind.
Secondly, we most often actually SEE Snape defending against or curing the effects of Dark Magic as well as he can. Snape counters the jinx on Harry's broomstick in the first book; Snape cures Dumbledore's hand as best he can, and deals with Katie Bell's curse before sending her to St. Mungo's. In fact, there are not one but two healers at Hogwarts: a good rule of thumb is that Madam Pomfrey deals with ordinary magical injuries, and Snape is called in when Dark magic is involved. Lupin, while he was DADA teacher, was the notable exception to this rule. Before the DADA position was cursed, it may have been an expected duty of the DADA teacher to deal with the effects of Dark Magic at Hogwarts.
There is an analogy in the muggle world. A doctor may be knowledgeable about a disease she combats, to the extent of actually admiring the way it works. A computer expert can appreciate an elegantly coded virus. And of course, a military officer can praise the prowess of his enemy. However, this does not mean the doctor wants to cause rather than cure the disease, that the computer person wants to write a virus, or that the military officer is ready to defect to his enemy.
The Dark Arts are complex, and require a great deal of skill to defend against. In Snape's chosen field, which is in fact to DO Defense against the Dark Arts, and only recently to TEACH it, he has an enemy (the Dark Arts, not just Voldemort) that calls forth all of his skill and inventiveness. Perhaps it is not the Dark Arts that Snape loves, per se, but the challenge of defending against them and reversing their effects.
Interestingly enough, we have seen three DADA teachers that have taught defense against the dark arts effectively, one of whom was definitely a current Death Eater: Lupin, Crouch and Snape. Of the three, Crouch, the Death Eater, is the only one who actually performed dark magic (and he even performed it regularly) in his classroom. Lupin and Snape both taught DEFENSE techniques. In fact, it may be true that the more knowledge you have of the Dark Arts, the LESS likely you are to perform them. With the possible exception of Dumbledore, no one else at Hogwarts has more experience dealing with the effects of Dark magic than Snape.