Small pairs exchange nothing and run, having doubts (8)
I believe the answer is:
scruples
'doubts' is the definition.
The definition and answer can be both related to thinking as well as being plural nouns.
Maybe you can see a link between them that I can't see?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for scruples that I've seen before include "Doubts stemming from conscience or principles" , "Feelings of doubt arising from conscience" , "Doubts or hesitations promted by conscience" , "Feelings of doubt produced by conscience" , "Doubts about the morality of an action" .)