For that reason Crichton for example draws distinctions inside the order of vesani first of all between the category of deliria, which alter the relation to truth that takes form in perception ('a general derangement of the mental faculties, in which diseased perceptions are mistaken for realities'), and the category of hallucinations, which alter representation: 'an error of mind in which ideal objects are mistaken for realities, or in which the real objects are falsely represented'; finally there is also the category of dementia which, without destroying the faculties that provide access to the truth, still sap their strength or weaken their powers.