Unforgivable Curses

"Never used an Unforgivable Curse before, have you, boy? You need to mean them, Potter!"

- Bellatrix Lestrange to Harry Potter

The Unforgivable Curses are the three most powerful and sinister spells known to the wizarding world, and are tools of the Dark Arts. They were made illegal in 1717.

Using any of these three curses on another human being carries the punishment of a life term in Azkaban. Aurors were permitted to use them during the First Wizarding War. Under Lord Voldemort's regime in 1997-1998, the curses were made legal.

Use
"Avada Kedavra's a curse that needs a powerful bit of magic behind it - you could all get your wands out and point them at me and say the words, and I doubt I'd get so much as a nosebleed."

- Barty Crouch Jr, disgused as Alastor Moody, to a Defence Against the Dark Arts class

Since the Unforgivable Curses are very powerful, their use requires both great will power and great skill in order to bring about the effects. For example, Harry Potter was unable to cast the Cruciatus Curse on Bellatrix Lestrange in 1996 because, despite being furious with her for her murder of his godfather, he lacked the desire to cause pain for its own sake. His "righteous anger" only inflicted a brief moment of pain on her.

Avada Kedavra - The Killing Curse

 * Description: Causes instant death.

The incantation of Avada Kedavra causes a bolt of blindingly intense green light to shoot from the end of the caster's wand, which, on contact with the victim, results in instantaneous death. There are no secondary effects; the victim simply "drops dead" for no biological reason. It is possible that the victim's internal organs cease function. Muggle coroners would be unable to find a cause of death in such an attack, but the Ministry of Magic recognises the signs of the curse.

The Killing Curse has no counter-curse or blocking spell, although the green bolt may be dodged or blocked with solid objects. For instance, Albus Dumbledore once transfigured a statue from the Fountain of Magical Brethren to shield Harry Potter from Voldemort's Killing Curse during the Battle of the Department of Mysteries. If the curse misses the victim and strikes an inanimate object instead, a small explosion at the point of impact results, which may start a fire of green flame.

The Killing Curse was used regularly by Lord Voldemort, possibly more than any other spell, and his Death Eaters used it as well. The spell is performed verbally as a rule; Bellatrix Lestrange killed a fox with a non-verbal spell after Apparating with Narcissa Malfoy at Spinner's End, thinking that it was a lurking Auror, but it is unknown whether it was Avada Kedavra or some other lethal curse.

Only one person has ever been able to defeat the effects of the curse, even on a direct hit: Harry Potter, who was given magical protection against Lord Voldemort's use of the curse through his mother's loving sacrifice. Harry was later saved by the effects of Priori Incantatem when his and Voldemort's wands locked during a duel in 1994. When Voldemort struck him with a Killing Curse again in 1998, Harry was able to survive again because Voldemort had taken some of Lily Potter's protection of Harry into his own body by using Harry's blood in his rebirth ritual in 1995.

In 1996, Fawkes sacrificed himself by swallowing a Killing Curse that Voldemort aimed at Dumbledore. Phoenixes respond to the Killing Curse the same way as they would to any other means of death: they are consumed by fire, and are reborn from the ashes.

Etymology
Avade kedavra stems from archaic Sanskrit words meaning "From life, nothing". It has the opposite root meaning of the phrase "Abra Cadabra", which means "From nothing, life".

Crucio - The Cruciatus Curse

 * Description: Inflicts excruciating pain on the recipient of the curse.

The Cruciatus Curse, which inflicts excruciating pain upon the victim, requires the verbal incantation and the use of a wand. The effects of the curse depend upon the desires and emotions of the character - to produce the excruciating pain implied by the name, one must, according to accomplished caster Bellatrix Lestrange, desire to cause pain purely for its own sake. The extreme pain inflicted by the curse makes it uniquely suited as a form of torture, and was used regularly by the Death Eaters."you dont need 1000 knives if you know the curciatus curse"

The Cruciatus is the curse which caused Alice and Frank Longbottom such suffering that they were admitted to the permanent ward at St. Mungo's Hospital for Magical Maladies and Injuries for insanity. This was carried out by Barty Crouch Jr and Bellatrix, Rodolphus and Rabastan Lestrange.

Etymology
Crucio stems from the first conjugation Latin verb "crucio, cruciare", which means "to torture or torment". The name of the curse, the cruciatus, stems from the Latin noun "cruciatus" which means torture.

Imperio - The Imperius Curse

 * Description: Causes the victim to perform the unquestioned bidding of the caster.

The Imperius Curse places the victim in a trance or dream-like state, leaving him or her under the complete control of the caster. The experience is described as a "wonderful release" from any sense of responsibility. The victim is relaxed, and carefreeingly obeys any order, from doing things they would be physically incapable of otherwise to committing horrible crimes. For example, Barty Crouch Jr, while disgused as Alastor Moody, had Neville Longbottom perform a series of astonishing flips under the Imperius Curse. Death Eaters have made use of this curse; for instance, in forcing Broderick Bode and Sturgis Podmore to try to steal a prophecy from the Department of Mysteries and to place several officials under their control to facilitate their take-over of the Ministry of Magic in 1997. Many Death Eaters also claimed to be under the Imperius Curse during the First Wizarding War to avoid imprisonment.

Resisting the Imperius Curse is possible, but extremely difficult. Only those of particularly strong will can acheive it. Harry Potter, Barty Crouch Sr and Barty Crouch, Jr each learned to resist the curse after being subjected to its effects.

Behind the scenes
The three curses seemed to be called "unforgivable" because they carry an automatic life sentence in Azkaban. The name may also allude to the concept of unforgivable sin (also known as "eternal sin" or "unpardonable sin") in Christian theology, an act that makes salvation impossible.