Although discussions of multimodality involve medium and mode, these two terms are not synonymous.
Gunther Kress's scholarship on multimodality is canonical in writing studies, and he defines mode in two ways.
Graphic resources can be broken down into font size, type, etc. In Kress’s theory, “mode is meaningful: it is shaped by and carries the ‘deep’ ontological and historical/social orientations of a society and its cultures with it into every sign.
Mode names the material resources shaped in often long histories of social endeavor.” Modes shape and are shaped by the systems in which they participate.
Writers often conceptualize their work by non-alphabetic means, through visual imagery, music, and kinesthetic feelings.