2. KEY CONCEPTS 2.1 Definition of torture The most widely accepted internationally agreed definition of torture is set out in Article 1 of the United Nations Convention against Torture and other Cruel, Inhuman or Degrading Treatment or Punishment (UN CAT): “ ...'torture' means any act by which severe pain or suffering, whether physical or mental, is intentionally inflicted on a person for such purposes as obtaining from him or a third person information or a confession, punishing him for an act he or a third person has committed or is suspected of having committed, or intimidating or coercing him or a third person, or for any reason based on discrimination of any kind, when such pain or suffering is inflicted by or at the instigation of or with the consent or acquiescence of a public official or other person acting in an official capacity. It does not include pain or suffering arising only from, inherent in or incidental to lawful sanctions.” See http://www.irct.org/what-is-torture/defining-torture.aspx for the complete text of the UN CAT. This definition contains three cumulative elements: • The intentional infliction of severe mental or physical suffering, • by a public official, who is directly or indirectly involved, • for a specific purpose. This definition raises the question of how to classify and respond to acts failing to meet all three criteria. For instance, what about an act that is not inflicted intentionally but occurs because of negligence? What if an act does not occur for a specific purpose? What if an act inflicts pain or suffering which is not considered severe? 
In these situations the prohibition of other forms of cruel, inhuman or degrading treatment or punishment may apply. As with torture, this prohibition is also absolute and non-derogable. (For further reference see: http://www2.ohchr.org/english/law/cat.htm) The prohibition of torture and cruel, inhuman or degrading treatment or punishment is absolute to ensure harm can never be justified under any circumstances whatsoever. Customary international law - which applies to all States, including those that have not ratified relevant human rights or international humanitarian law treaties - considers the prohibition of torture to be a peremptory norm, or jus cogens. In other words, no exception or derogation to the prohibition is permitted in any circumstance, even a state of war, the threat of war, internal political instability or public emergency. Necessity, self-defence and other defences are not accepted in any case of torture, no matter how extreme or grave the circumstance. Relevant international treaties unanimously exclude the freedom from torture and ill-treatment from derogation and restriction clauses. 6