Course for a fool turned philosopher (7)
I believe the answer is:
passage
'course' is the definition.
(I've seen this before)
'fool turned philosopher' is the wordplay.
'fool' becomes 'sap' (synonyms).
'turned' shows that the letters should be reversed in order.
'philosopher' becomes 'sage' (sage can mean a wise person).
'sap' back-to-front is 'pas'.
'pas'+'sage'='PASSAGE'
'for a' is the link.
(Other definitions for passage that I've seen before include "course" , "Literary extract" , "Transit - part of book etc" , "Sea/air journey" , "Section of text; journey" .)