One trades in ethical concepts (6)
I believe the answer is:
ideals
'ethical concepts' 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?
'one trades' is the wordplay.
'one' becomes 'i' (Roman numeral).
'trades' becomes 'deals' ('deal' can be a synonym of 'trade').
'i'+'deals'='IDEALS'
'in' is the link.
Can you help me to learn more?
(Other definitions for ideals that I've seen before include "Standards of excellence" , "Models of excellence" , "Moral standards" , "Moral value" , "'Perfect models, highest notions (6)'" .)