Full Idea
So long as we are ignorant of the true essence of the cause which is operating, we call it a 'faculty'.
Gist of Idea
We just use the word 'faculty' when we don't know the psychological cause
Source
Galen (On the Natural Faculties [c.170], I.iv), quoted by Dominik Perler - Intro to The Faculties: a History 2
Book Reference
'The Faculties: a history', ed/tr. Perler,Dominic [OUP 2015], p.9
A Reaction
This is probably the view of most modern neuroscientists. I want to defend the idea that we need the concept of a faculty in philosophy, even if the psychologists and neuroscientists say it is too vague for their purposes.