The logic of hearing, say (5)
I believe the answer is:
sense
I believe this clue is a double definition.
'the logic' is the first definition.
(I've seen this before)
'hearing say' is the second definition.
(hearing is a kind of sense)
'of' is the link.
(Other definitions for sense that I've seen before include "Comprehend" , "Realistic attitude" , "smell, for example" , "Feeling or faculty" , "Feel intuitively" .)