If I were a lawyer trying to persuade a jury that Macbeth was insane, I would initially focus on the irrationality of Macbeth killing Duncan in the first place. Duncan had just recently rewarded Macbeth with a title for his courage in battle. Macbeth had every reason to hitch his star to a king who had always been good to him. Who but an insane person would cut off such patronage and bite the hand that fed him so well?
Second, who but an insane person would trust the cryptic words of three weird witches? That, in and of itself, seems insane. Why not as well trust the rustle of the wind seeming to tell you that you should murder your king?
Third, who, in the context of the times, would murder the king they were bound to protect in their own home? Such a severe violation of the hospitality codes of that era seems insane. Regicide, too, is a potentially insane act. Killing a king, appointed by God to rule, and a good king at that, is one of the worst sins anyone could commit. What rational person...
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