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In short, herein seems to lie the difference between idiots and madmen, that madmen put wrong ideas together, and so make wrong propositions, but argue and reason right from them: but idiots make very few or no propositions, and reason scarce at all.

John Locke (1828). “An essay concerning human understanding ... The twentieth edition, etc”, p.100
In short, herein seems to lie the difference between idiots and madmen, that madmen put wrong ideas together, and so make wrong propositions, but argue and reason right from them: but idiots make very few or no