The difference is writing as part of one's career (at the direction of supervisors) and writing at one's own discretion. If your school says "yo, prof! Write a

The difference is writing as part of one's career (at the direction of supervisors) and writing at one's own discretion. If your school says "yo, prof! Write a book on $subject," then it's a work-for-hire and, if public money is involved, should be public domain. If the professor takes it upon himself to write a book, presumably on hus own time, he then holds the copyright.