Mediaeval philosophers accepted the ten categories in Aristotle’s Categories: substance, quantity, quality, relation, time, place, action, passion, position, and state or having. They wondered, however, whether categories were categories of concepts or words or things, on what basis one could arrive at all ten, and whether Aristotle’s list was exhaustive. Chatton addresses a number of questions about categories, positioning himself between Scotus and Ockham. While Scotus argues that the categories are primarily ontological – there are ten basic extra-mental essences or natures – and secondarily semantic (conceptual and linguistic), Ockham argues that the categories are purely semantic. Like Scotus, Chatton holds that there are ten basic classes of things, but like Ockham, Chatton insists that the categories are ten kinds of terms. What is notable about Chatton’s contribution to theories of categories is that he uses the Chatton Principle to argue for the ontological classes that underpin the categories.