  The notion of a being of reason, or more specifically the notion of a relation of reason, does not appear to have been invoked in the Latin West before the thirteenth century, when Aristotle’s Metaphysics and certain Muslim philosophical commentaries and treatises derived from it began to circulate widely. The notion of a relation of reason is not to be found explicitly in the works of Aristotle, though he does distinguish beings of reason in general from real beings (cf.  Metaphysics IV, 1, esp. 1003a32–b11 and V, 7, esp.  1017a31–35). Even so, this notion is explicitly invoked by certain Muslim philosophers, most notably Avicenna (d. 1037), and it may well be that it makes its way into the Latin west through them.