What is 'Dark Magic'?

[Jim Ferer]

No: HPFGUIDX 95861

Potioncat: So, it's OK if he didn't inhale? Or if he didn't "go all
the way?"
I've avoided this topic because it's gotten very deep, and it's hard
to tell if it is what JKR intended. But if indeed, Dark Magic is magic
that somehow harms/changes the caster as well as the victim, then
Harry was most likey affected in some way. The fact that it failed
doesn't change the fact that he cast it."

The point is not that Harry took no lasting harm because the curse
failed; the curse failed because his heart wasn't in it, he didn't
really want to see suffering – certainly not in the psycho way
Bellatrix does.

Your cigarette analogy is apt, and I would say in the same vein that
Harry might have tried it once, but he's very unlikely to actually
take up smoking.  Someone else might be more vulnerable.
Potioncat:"Boy, did I have a great idea on this one. Canon blasted it,
however! Jim, do you recall who said Parseltongue was dark magic? In
"The Dueling Club" pp 195--197 Hermione, Ron and Harry discuss it.
They say it is bad. But they also think it ties him to Salazar
Slytherin. It is actually hard to tell if they think Parseltongue
itself is bad,(my original impression) or if being related to
Slytherin at that particular time is bad.  But the phrase Dark Arts
never comes up in that section."

You're right, but the exchange I'm thinking of came a couple of pages
later, when Ernie Macmillan and his friends were whispering together
in the library:

"Hannah," said the stout boy solemnly, "he's a Parselmouth. Everyone
knows that's the mark of a Dark wizard. Have you ever heard of a
decent one who could talk to snakes? They called Slytherin himself
Serpent-tongue."

So I'm sticking with the notion that it's the state of mind of the
caster that's the most important element in Dark Magic.  BTW, if you
can find it, find the late Randall Garrett's Lord Darcy stories,
mysteries set in an alternate history where magic works.  Garrett knew
a great deal about literature about magic and the Laws of Magic and
put it into his stories.  They're great reads anyway, and you'll find
his ideas affecting yours, I bet.

Jim Ferer