The territory under the jurisdiction of a state would ordinarily be understood as being the territory over which it has de jure control. If torture carried out by insurgents in territory under their de facto control falls within the scope of UNCAT, it follows that article 2(1) imposes an obligation on states with which they cannot comply: they cannot take “effective” measures in relation to territory which they do not control. UNCAT cannot sensibly be interpreted in a way which would have the effect of imposing an obligation on states with which they cannot comply: lex non cogit ad impossibilia. That strongly suggests that article 2(1) cannot have been intended to apply in those circumstances, which in turn implies that the definition of torture in article 1 cannot have been intended to apply to torture committed by insurgent forces, without the consent or acquiescence of the state in question. 86. Thirdly, article 31(1) of the Vienna Convention requires a treaty to be interpreted “in the light of its object and purpose”. UNCAT is intended, as its preamble recites, “to make more effective the struggle against torture and other cruel, inhuman or degrading treatment or punishment throughout the world”. Nevertheless, by the time UNCAT was concluded, the prohibition of torture was already recognised as a peremptory norm of international law, enshrined in article 7 of the International Covenant on Civil and Political Rights (ICCPR). The objective of UNCAT, as appears from its substantive provisions, was more specific: to impose obligations on states actively to prevent and punish torture, including by means of universal jurisdiction. Thus, as I have explained, article 2 requires states to take effective measures to prevent acts of torture, as defined in article 1, in any territory under their jurisdiction. Article 3 prohibits states from expelling, returning or extraditing persons to other states where they are liable to be tortured. Articles 4 to 9 make provision for states to exercise an extra-territorial jurisdiction in respect of acts of torture, requiring them to prosecute persons within their jurisdiction who are alleged to be responsible for torture, wherever it occurred, and to punish them if convicted. It is for the purpose of those obligations that article 1 adopts a definition of torture which is specifically concerned with the conduct of public officials and other persons acting in an official capacity: a definition which is narrower than the concept of torture in the ICCPR (or in other international law instruments, such as common article 3 of the Geneva Conventions, the Rome Statute of the International Criminal Court, or the statutes of the International Criminal Tribunal for the Former Yugoslavia and the International Criminal Tribunal for Rwanda). 87. Articles 4 to 9 of UNCAT, in requiring states to exercise a universal jurisdiction in respect of acts committed in other states and having no connection to themselves, are particularly significant in international law, since they make inroads into national sovereignty. Two implications follow. First, if there is a real doubt as to the interpretation of article 1, it is more likely, other things being equal, that the states parties will have intended a narrower rather than a more expansive reading, since they are unlikely to have intended to diminish their sovereignty further than they had made reasonably clear. Secondly, one would expect there to be a Page 42