Commentary published in its own volume can be cited as a work in itself. In the multivolume translation of Dante’s Divine Comedy cited below, each part of the work occupies one volume supplemented by a separate volume of commentary.

The entry for the translation of part 1, Inferno, names Dante in the Author element:

Dante. Inferno 1: Text. Translated by Charles S. Singleton, Princeton UP, 1990. Vol. 1 of The Divine Comedy.

But the commentary volume can be listed under its author’s name:

Singleton, Charles S. Inferno 2: Commentary. Princeton UP, 1990. Vol. 2 of The Divine Comedy.

More often than not, however, a commentator is an editor who is listed in the Contributor element:

Brontë, Charlotte. Jane Eyre. Edited by Richard J. Dunn, Norton Critical Edition, 3rd ed., W. W. Norton, 2001.

For more information on citing contributors, see sections 5.38–5.47 of the MLA Handbook (145–54). For guidance on citing individual volumes from multivolume works, see section 5.117 (215–16).  

Work Cited

MLA Handbook. 9th ed., Modern Language Association of America, 2021.