Walter Chatton or more rarely “Catton” (c. 1290–1343) was an English theologian and philosopher who trained at Oxford around the same time as his famous colleague and frequent philosophical target, William of Ockham. More inclined to speculative metaphysics and less skeptical of reason than Ockham, Chatton was one of the most energetic and gifted critics of the influential brand of nominalism which arose in early fourteenth-century England around Ockham. As a constructive philosopher, Chatton was not a system-builder, but a defender of certain parts of the more systematic philosophy of John Duns Scotus, and an advocate of perspectivist accounts of cognition. Historically he is an interesting figure because he combined the realist tendencies of Scotism with the appreciation of logic and language we see in Ockham; thus it is common to find Chatton defending Scotistic theses and criticizing Ockham using the same sorts of semantic ideas that Ockham himself popularized. His unyielding attacks on Ockham bore him fruit intellectually and otherwise: we have evidence of Ockham changing his mind on several seminal issues as a direct result of Chatton’s critiques. Moreover, he seems to have built a very successful ecclesiastical career, no doubt based in part on his cleverness; he served as an advisor to two popes, and earned for himself, but did not live long enough to enjoy, a bishopric in Wales. His stature as a theologian rose high enough in his lifetime that his opinions on sacramental efficacy were remembered and cited at the Council of Trent, two hundred years after his death.