Section 320(1)(b) of the Crimes Act 1900 (ACT) restates the Porter test: 'wrong' means morally wrong by the standards of ordinary reasonable people, not merely contrary to law. Where an accused suffering from paranoid schizophrenia acts under delusional beliefs creating a perceived moral dilemma (believing killing is the lesser of two evils), the accused may be incapable of understanding the moral wrongness of the act even though aware it is legally wrong.
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