An abnormal state of mind that does not constitute insanity (R v Seers  79 Cr App 261 CA) but is a partial defence to a charge of murder. The abnormality of mind (which need not be a brain disease) must substantially impair the mental responsibility of the accused for his acts, i.e. it must reduce his powers of control, judgment, or reasoning to a condition that would be considered abnormal by the ordinary man (R v Byrne  2 QB 396). It may be caused by disease, injury, or mental subnormality, and is liberally interpreted to cover such conditions as depression or irresistible impulse (R v Vinagre (1979) 69 Cr App R 104). If the defendant proves the defence, he is convicted of manslaughter. See also Battered Woman Syndrome; domestic violence.