Writing possibly penned by top philosopher (4)
I believe the answer is:
marx
'philosopher' is the definition.
(Karl Marx)
'writing possibly penned by top' is the wordplay.
'writing possibly' becomes 'R' (one of the traditional three R's of education).
'penned by' is an insertion indicator (inserted letters are penned in).
'top' becomes 'max' (short for maximum).
'r' going into 'max' is 'MARX'.
(Other definitions for marx that I've seen before include "The Economist" , "Harpo's surname" , "The Communist Manifesto author" , "Das Kapital author" , "Groucho's surname" .)