new edit, and nested routes

I am writing an application where a :subject has_many courses

For the new functionality, it makes sense to use new_subject_course(subject, course),

But for edit, do "best practices" say edit_course(course), or edit_subject_course(subject, course)?

Since course belongs_to subject, the code can find the subject without an explicit id passed in. However, using edit_subject_course makes the edit and new forms very similar.

Just wondering.