Citation, Documentation of Sources

Q. I am teaching my students CMOS notes and bibliography type for all of their academic papers. When using footnotes on a paper the student did the full bibliographic citation on page 1. Then on page 2 there was a reference to the same source. Is it correct to allow the student to simply use author-date for that subsequent citation? Or is it more correct for the student to repeat the full bibliographic citation?

A. Chicago prefers shortened citations after the first full mention. CMOS 13.21 and the examples that follow will give you a solid overview of notes-bibliography style that will help you teach your students. And our Citation Quick Guide includes examples of shortened citations (author, title, page) for each full note.

[This answer relies on the 18th edition of CMOS (2024) unless otherwise noted.]