Three unforgivable curses are as follows:
1. Killing Curse
2. Imperius Curse
3. Cruciatus Curse
I just wanted to know if what are the standards of classifying a curse as unforgivable.
Three unforgivable curses are as follows:
1. Killing Curse
2. Imperius Curse
3. Cruciatus Curse
I just wanted to know if what are the standards of classifying a curse as unforgivable.
Those aren't just three known Unforgivable Curses; they are by definition the three Unforgivable Curses. If you like, the standards for classifying a curse as unforgivable are "to be one of those three".
From when they're first introduced in the series, in HP and the Goblet of Fire:
"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. That’s what you’re up against. That’s what I’ve got to teach you to fight."
And according to Tales of Beedle the Bard:
The Cruciatus, Imperius and Avada Kedavra Curses were first classified as Unforgivable in 1717, with the strictest penalties attached to their use.
If the question is really 'why those three, and not others', then I think the (unspoken) within-canon answer may be that those three curses uniquely imperil the soul - both for the victim and for the caster. For the victim: (1) Flings the soul out of the world altogether, (2) Damages the soul by overriding free will, and (3) Damages the soul though unbearable pain [e.g witness the insanity of the Longbottoms]. For the caster, effective use of the curses requires the taking of pleasure in evil acts: (1) Murder, (2) Domination, and (3) Torture.