Student or Learner
Quote from a harvard open course :
"And a few years later, Kant wrote thegr oundwork for "Metaphysics of Morals" which we read in this course.
I want to acknowledge even before we start that Kant is a difficult thinker."
What does "difficult thinker mean here?
For me, it means that his thoughts were complex and, perhaps, will be difficult for students to understand. It's a little warning to students that they might be confused.
Note that Harvard should be capitalised.