Answered By: Julene Sodt Last Updated: Jul 28, 2016 Views: 45
The Chicago Manual of Style calls this kind of footnote "Substantive notes."
From CMS, section 16.54
Substantive, or discursive, notes may merely amplify the text and include no sources. When a source is needed, it is treated as in the example in 16.53 or, if brief and already cited in full, may appear parenthetically, as in the following example.
1. Ernst Cassirer takes important notice of this in Language and Myth (59–62) and offers a searching analysis of man’s regard for things on which his power of inspirited action may crucially depend.