However, pace what Reid has to say on the matter it seems to me that there is in fact something special about the rational faculty that sets it in sharp contradistinction to the sensory faculty. Specifically, there appears to be a unilateral relationship between the two faculties such that our rational deliberations can be employed to evaluate the reliability of our sensory deliverances, but our sensory deliverances cannot be used to evaluate our rational deliberations.
This claim is illustrated by the Ron Howard film, A Beautiful Mind, which is loosely based on the life of the mathematician and winner of the 1994 Noble Prize in Economics, John Forbes Nash. In the movie, Nash suffers from an extreme form of paranoid schizophrenia that gives rise to sensory experiences (both visual and auditory) of people, places and objects that do not exist. Nash’s hallucinations are phenomenally indistinguishable from actual objects. However, he learns to use his superior gifts of logical reasoning to figure out which phenomena are real and which are not. (For example, he is able to deduce that his supposed best friend Charlie was merely a hallucination by noticing small inconsistencies in his dress and in the way he aged.)
We have no problem imagining someone using their rational faculty to evaluate the veridicality of their sensory deliverances in the manner John Nash did. However, it only takes a moment’s reflection to realize that it would be absurd to talk about someone using their sensory faculties to determine whether or not their rational judgements are veridical. Thus, while we can imagine using reason to evaluate the reliability of the senses, we cannot imagine using our senses to evaluate the reliability of reason. I believe that this unilateral relationship between reason and the senses suggests that there is something unique about the rational faculty that sets it apart from the faculty of sense. I will refer to this thesis by saying that reason is sui generis vis-à-vis the senses. In my next post on this topic, I will develop my sui generis thesis further and respond to one possible objection to my proposal.