Old philosophy teacher's a pathetic person confusing this (7)
I believe the answer is:
sophist
'old philosophy teacher's a pathetic person confusing this' is the definition.
The definition suggests a singular noun which matches the answer.
'person confusing this' is the wordplay.
'person' becomes 'sop' (I can't explain this - if you can you should believe this answer much more).
'confusing' indicates anagramming the letters.
'this' is an anagram of 'hist'.
'sop'+'hist'='SOPHIST'
Can you help me to learn more?
(Other definitions for sophist that I've seen before include "One using clever but fallacious arguments" , "One who uses clever but false argument" , "one might plausibly argue" , "One given to specious reasoning" , "One using clever but wrong arguments" .)