Glosae

For all that has been said since the 1960s — with special and especially democratic dedication to the reader's  freedom  —  about  multiple  meanings  as  a  potential  of  any  individual  text  and  about interpretation  as  a  never-ending  task,  for  all  those  very  sophisticated  and  sometimes  overly  complicated pictures of the act of interpretation, I think that in our everyday practice we take interpretation as a task that can and normally will be brought to a conclusion. We expect that, in the average case of an interpretation, there will be a moment when we know that we have understood  the  text  or  other  artifact,  and  we  normally  associate  understanding  with  the impression  that  we  now  know  what  the  author  wanted  this  text  to  mean  or  be. 

This assumption  about  the  normally  finite  character  of  interpretation,  I  believe,  explains  its triumphant career as a core exercise for homework assignments and written tests in secondary education.  Commentary,  in  contrast,  appears  to  be  a  discourse  that,  almost  by  definition, never reaches its end. Whereas an interpreter cannot help extrapolating an author-subject as a point of reference of his or her interpretation (and cannot help giving shape to this reference as the interpretation progresses), a commentator is never sure of the needs (i.e., the lacunae in the  knowledge)  of  those  who  will  use  the  commentary.

However  carefully  you  cater  to  the needs  of  your  contemporaries  among  the  potential  readers  of  a  text  in  question,  you  can never anticipate exactly what will have to be explained for readers of the next generation, and it  is  mainly  this  condition  that  makes  commentary  a  constitutively  unfinished  exercise  and discourse.  Not  surprisingly,  then,  the  history  of  the  word commentary yields  too  many different meanings — and therefore too vague a meaning — to suggest a more precise definition. 

And does this general flavor of vagueness not go together with an impression that users of commentaries almost always have, namely (and to exaggerate only slightly), that any given commentary offers all kinds of interesting bits and pieces of knowledge but hardly ever  that  one  piece  of  information  that  you  needed and  whose  need  made  you  consult  the commentary in the first place?

Hans Ulrich Gumbrecht. The Powers of Philology. University of Illinois Press (2003).