Learnt from chain letters this is a study of moral philosophy (6)
I believe the answer is:
ethics
This could be a double definition.
'learnt from chain letters this is a study' is the first definition.
The definition suggests a singular noun which matches the answer.
'moral philosophy' is the second definition.
(synonyms)
'of' is the link.
Can you help me to learn more?
(Other definitions for ethics that I've seen before include "Science of moral principles" , "Science of morals" , "Some philosophy" , "Codes or principles for professional people" , "rules of conduct" .)