Definition: "grammar, rhetoric, and logic," the first three of the seven liberal arts in the Middle Ages, considered initiatory and foundational to the other four: arithmetic, geometry, astronomy, and music.

Etymology: From Latin "trivium," tri (three) + via (road); a place where three roads meet.

Wikipedia has it broken down as "grammar, logic, and rhetoric" = "input, process, and output." This is pretty consistent with Enlightenment thinking that logic is the process and rhetoric is the presentation. I'm interested in how this gets appropriated to a trivium of "syntactics, semantics, and pragmatics."