At this point we might ask what licenses us to conclude that the entity whose existence Chatton proves is indeed a res? Can’t propositions get to be true and false for other reasons besides a res coming to be or passing away? Chatton did not think they could, at least in most cases, and his Principle exhibits this commitment in version (2) above; the only way to add to an ontological snapshot is to add things (res) to the picture. Hence he relies on and is clearly committed to an assumption which says that if an existent makes a difference to truth then it must be a real thing (res). This assumption can be found in Aristotle (e.g., Physics, 225a 1–20) and Scotus (e.g., Ordinatio I d. 30 qq. 1–2, n. 41). Often called the principle of contradictories, it can be stated as follows: “There can be no passage from contradictory state to contradictory state without the generation or corruption of some thing (res).”