Citation, Documentation of Sources

Q. Hello, I use old-style figures in the text of my document. Do you have any recommendations for whether they should then be used also for footnote markers in the body text and/or the footer?

A. Our designers prefer lining figures for the superscript note reference numbers in the text, even in works that otherwise feature old-style figures—as in the book Eleanor of Aquitaine, as It Was Said: Truth and Tales about the Medieval Queen, by Karen Sullivan (University of Chicago Press, 2023). The corresponding numbers at the beginning of each note, however—which in Chicago style aren’t superscripts—would use old-style figures.

Superscript lining figures in the text:

Snippet from text of book showing lining figure for superscript note number 106.

Old-style figures on the baseline in the corresponding note:

Snippet of an endnote from a book showing old-style note number 106.

Notice how the digits in the superscript 106 are all roughly the same height, ensuring that a note number 1, for example, will be about the same size as a note number 6. This matters more with the smaller superscripts than it does for the numbers that sit on the baseline—even in the text of the notes, which is slightly smaller than the main text. (The Sullivan book features endnotes, but the advice would be the same for footnotes. See also CMOS 14.24.)

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]