DELUSION, med. jurisp. A diseased state of the mind, in which persons believe things to exist, which exist only, or in the degree they are conceived of only in their own imaginations, with a persuasion so fixed and firm, that neither evidence nor argument can convince them to the contrary.
2. The individual is, of course, insane. For example, should a parent unjustly persist without the least ground in attributing to his daughter a course of vice, and use her with uniform unkindness, there not being the slightest pretence or color of reason for the supposition, a just inference of insanity, or delusion, would arise in the minds of a jury: because a supposition long entertained and persisted in, after argument to the contrary, and against the natural affections of a parent, suggests that he must labor under some morbid mental delusion. 3 Addams' R. 90, 91; Id. 180; Hagg. R. 27 and see Dr. Connolly's Inquiry into Insanity, 384; Ray, Med. Jur. Prel. Views., §20, p. 41, and §22, p. 47; 3 Addams, R. 79; 1 Litt. R. 371 Annales d'Hygiene Publique, tom. 3, p. 370; 8 Watts, 70; 13 Ves. 89; 1 Pow. Dev. by Jarman, 130, note Shelf. on Lun. 296; 2 Bouv. Inst. n. 2104-10.