"What, exactly," I ventured, "makes 'Dark' magic dark?"

Celestia and I were sitting on the viewing gazebo of the highest tower, enjoying one another's company and the view of the world stretched out before us and discussing this and that. Eventually the subject had drifted around to the topic of the Equestrian's exotic science, and I had been moved to raise this question.  "That's... an interesting question, Arthur," Celestia said, tilting her head. "What brings this up?"

I pooched out my lip, trying to compose my answer. "In... spite of having no magic in our world, humans have a lot of different... theories, I suppose you'd say... about how it would or might work."

"So I have gathered from your works of fiction," Celestia said, amused. "Coincidentally, would it make you feel more comfortable to call it 'Quintessence manipulation' rather than 'magic?' That is the proper scientific term for it after all, and I do know that your people conflate the word 'magic' with witchcraft... "

I waved it off. "Perhaps-- but that's a topic for another time," I said, shaking my head. Occultic bastards, hijacking the language for their own ends...  "but let's use the common Equestrian word for the sake of the subject at hand."

"Very well."

"As you say, human culture has multiple 'magic systems' in its fantasy writing," I went on. "And most of them incorporate the idea of 'light' and 'dark' magic, though the definition of what makes it light or dark varies from author to author. In some, it is determined by what source you draw the power from--- holy beings and angels or dark powers and demons. In some it is defined by what tools and ingredients are used, say between using herbs and crystals versus using the blood of virgins and other ghastly things. In others it's defined by whether the spells are healing and passive and defensive, or aggressive and injurious. In still others (the most common, I would estimate) the light side is powered by  being at peace and tranquil , while the dark side is powered by passion and negative emotions...."

"It seems that the exercise tells you less about the actual nature of 'magic' than it does about the moral philosophies of the writers," Celestia noted with mild amusement.

"True," I nodded. "While here in Equestria, the situation is the inverse. I have seen ponies and others use what they term 'Dark' magic... which, depending upon how it works, could be expected to inform your moral philosophy."

"Ah," Celestia said, chuckling. "And you wish to know, thereby giving you a peek into what makes us 'tick', so to speak."

"Partially," I admitted.

"First, though, I'm curious about that 'light side, dark side' fiction you mentioned," Celestia said. "It comes from that 'War Stars' series, as I recall?"

"Close enough," I chuckled. "Is that the closest approximation to--?"

Celestia huffed. "No no, far from it," she said. "It's a bloody ridiculous notion." At my raised eyebrow she continued. "Arthur, there's no such thing as  inherently 'good' or 'evil' emotions. That's something I've struggled to hammer into my students' heads over the millennia. Anger, sorrow, and fear are not "negative" emotions. They are not intrinsically "bad" or "evil." They are necessary and vital to our survival. Any creature that does not feel fear doesn't survive past infancy, because they're standing there gormlessly indifferent to oncoming danger when sane, healthy creatures are shying back or running away.  And anger... well, there is such a thing as righteous anger, and the world sorely needs more of it.

"Meanwhile the most horrible deeds--- from crimes of passion to the slow pushing of entire civilizations into oppression and slavery-- are done in the name of "love." "

I nodded, and quoted C.S. Lewis. “Of all tyrannies, a tyranny sincerely exercised for the good of its victims may be the most oppressive. It would be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated; but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience."

Celestia nodded in agreement. "Good and Evil are not feelings. They are actions, choices, and deeds. While unreasoning passions may make committing errors more likely, they do not lend them any special power or grace them with any extra vice. Sufficient to the deed is the evil thereof."

I nodded. I had been unable to quite put my finger on what bothered me so much about George Lucas' dualistic fictional philosophy, but in retrospect it was obvious. "So, to bring it back to the original question, what makes Dark magic Dark?" I asked.

"That's rather simple actually," Celestia said. "It's place on the spectrum."

I furrowed my brow. "Pardon?"

Celestia saw me foundering and moved to explain. "As you know, the ancients believed that the universe was made of four elements-- Earth, Water, Air and Fire," she reminded me. "Of course modern science has abandoned the superstitious nonsense of 'earth, fire, air, and water' and replaced it with 'solid, liquid, gas, and plasma/energy.' Hurray for scientific progress." She rolled her eyes and smirked and I snickered.

"Equestrian 'magic' involves the manipulation of Quintessance, or the Fifth Element, that the ancients believed both transcended and underlay the other four.... or what modern Equestrian physics calls the fifth, transcendant state of matter." she hesitated, waving a hoof. "Well there is some argument on that issue-- some say it is a hyperdimensional state of matter, others argue that it is closer to a form of energy at dimensional right angles to our own material universe. Others have still stranger explanations that even I fumble to grasp."

"Something like the argument over light being waves, particles, and/or both," I said.

"Something like that. Once the researchers start describing the universe with things like 'Multiply the square root of infinity by a carrot' I give up and just smile and nod. Anyway, we use Quintessence to manipulate the material universe around us, via the morphic resonance field.... and I just lost you too, didn't I." She shook her head. "Anyway, we use Quintessence. And Quintessence has a number of exotic properties, including what you might call wavelength."

"Ahh, I think I see where this is going."

"You've surely noted the rather colorful nature of Equestrian magic. Most normal magic is conducted within the fairly broad middle ground-- by pulling and manipulating Quintessance in the 'middle' spectrum, which tend to produce effects in the usual rainbow colors.

"But outside that band lies what you might think of as the ultraviolet and infrared of quintessance energy.... the 'dark' spectra. They tend to produce effects in the indigo and dark umber..."

"The purple-black of Sombra's magic," I contributed. "Or the extremely dark red of the Alicorn Amulet."

Celestia nodded. "Quintessence in those wavelengths isn't innately 'evil,' any more than infrared and ultraviolet light are. In fact it has certain highly useful and exotic properties that are much harder to get out of the harmonic rainbow band. In many ways it's easier to use, even. " She frowned, sipping her lemonade. "But it does have certain negative effects, especially if over-used...

"Ponies are designed to use the rainbow bandwidth. When they start dipping into the Dark spectra, indigo or umber, it is initially physically and psychologically unpleasant. But it gives a massive power boost-- plus, over time, feelings of euphoria. A sense of invincibility. hampered judgment and risk assessment.  Increased aggression...."

"Like a performance enhancing drug," I said, immediately grasping the implication. This, I had to admit, was utterly fascinating; A magic system where "light" and "dark" were not innate ethical or moral poles, yet where a definite ethical issue was present.

"And it becomes more and more addictive, the more it is used." Celestia said. She looked, brooding, into her glass. "alicorns have some resistance to it. But... after what happened to poor Luna... I have had to reevaluate how much resistance we have. It's so dangerous."

"And illegal as hell, I would presume," I said.

Her answer startled me. "And what good would that do?" she said, with a surprisingly ungenteel snort. "Tapping into Dark quintessence is esoteric knowledge, but in the end it is merely a matter of learning to reach up or down the wavelengths. But to outlaw it entirely would border on an unenforceable law. It would be like trying to criminalize the color blue."

She stirred her ice with her straw. "There are mountains of restrictions on it, of course. And we quite bluntly use folklore and propaganda to teach ponies to fear its touch and shun its use...not difficult, considering its more unpleasant side effects... and the crown refuses all funding for its research. But, there are times when it is necessary. Or simply too useful. Times when I've had to use it myself." She shuddered. "Extreme wavelengths of Quintessence can achieve certain effects that the safer bandwidths cannot. And sometimes it is necessary to use Dark magic in order to undo its effects."

"Like... using radiation therapy to destroy tumors?" I fished for a metaphor.

"I believe that's one possible parallel," Celestia agreed. She didn't look up from her glass. "But researching it is so dangerous...one must exercise iron self-control, rigid temperance. To study it one must use it after all, and use exposes oneself to potential addiction and corruption.

"After Nightmare Moon, I did outlaw it. For at least a century, I think. Then the Black Blight happened and I had to relent... It took some poor foal nearly dying of the Blight at my hooves before I realized my folly. I was blaming the substance for the sin of the abuser. The hardest thing I ever did was force myself to open up my magic and use Dark quintessence again to--" she cut herself off.

Again. I had one of my brief, rare moments of inspiration. A younger sister, driven by jealousy to abuse a performance-enhancing substance. A guilt-ridden older sister, blaming herself far too much... Nightmare Moon wasn't just a villain. She had been a drug addict.

"Luna learned to use Dark magic from you," I said. "Didn't she." Celestia said nothing. "When you were much younger, I suspect. She saw you use it for something. Or caught you at it. Whatever."

Celestia set her glass down on the arm of her divan and looked away, a thousand year old hurt on her face. Hurt and anger at herself. "And talked me into showing her how to tap into it. We were very young, barely more than foals. I dabbled. I forswore its use for fear of what might happen.

"And then King Sombra happened." Her jaw clenched. "I can only assume she saw how monstrously powerful this mere unicorn had become with its use, and decided to assuage her jealousy of me by...enhancing herself with it to finally outdo me, to surpass me... remembered my own use of it, found my discarded tomes."

I rested one hand on her withers, trying to console her. An older sister, blaming her own experimenting for her younger sibling's fall into a terrible addiction. She regained her composure. "It causes her physical pain now to use Dark magic," she said. "Whether that is the influence of the Elements, or simply a consequence of..."

"Going cold turkey?"

"What an odd turn of phrase. Either way, we are both grateful for that... extra obstacle to temptation. Still, it's always going to be there. It is for every pony who gains great power, or who tastes a bit of dark magic. But for her--"

"We are all guilty of our own sins," I said. "She doesn't blame you for what happened. Neither should you."

"I... suppose, I..." She picked up the pitcher before her and topped off our glasses. "Thank you."

"You're welcome," I said. I lifted my glass to her, then paused. "Your majesty, I think you should lift the research ban. In fact, I think you should dedicate some funds to a Dark Magic research lab."

She started to bristle. I had to tread carefully;  taken the wrong way this could come across like suggesting government funding of dope farming. "Your majesty, you say it's impossible to completely outlaw, because it is so easy for an amateur to simply stumble across by... by turning the radio dial far enough in one direction, in essence. You say the stuff, for all its side effects, is useful, as well as physically harmful and potentially addictive. You also say that it is not inherently evil-- that it's just another form of Quintessence.

"But save for some assuredly contraband books by those who ignored the taboos, we are working in a knowledge void when it comes to the stuff. That's not position from which anyone should be setting policy or making legislation."

"Power is power," she admitted. "Whether it comes from a horn or a light socket."

"In which case, have you tried to make it come from a light socket?" I pressed on at her querying look. "That is to say--- have your researchers tried manipulating the stuff using mechanical means? I know they've been able to research harmonic magic in this manner already, generating it with crystal arrays...and considering all the Quintessence the pegasi pump around the weather factories, it's obviously feasible.  They should be able to adapt the technology to Dark magic, shouldn't they?...

Offer a grant to researchers. If they can demonstrate they can do indirect research, take them on board. they might make all manner of discoveries without risking themselves. Perhaps even a way to neutralize its negative effects." It made sense to me; we humans made a lot more progress understanding radiation when we learned not to handle radioisotopes with our bare hands.

"An idea, perhaps," she said. "We cannot make use of it, or even effectively combat it, if we do not understand it better. I will take the idea under advisement." She mulled it over.

"Well," I said. I raised my glass to her. "One hopes for the best. Here's to a conversation that has proven most... illuminating." She smiled and tapped the rim of her glass to mine.