Cite as the guiding principal of taste (9)
I believe the answer is:
aesthetic
'taste' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'cite as the guiding principal' is the wordplay.
'cite as the' can be anagrammed to 'AESTHETIC'.
But, I am unsure how this is indicated.
'of' is the link.
Can you help me to learn more?
(Other definitions for aesthetic that I've seen before include "Of pleasing appearance" , "Concerned with the appreciation of beauty" .)