 His main concern in the first book is to simplify the Aristotelian-scholastic apparatus. For Valla, the world consists of things, simply called res. Things have qualities and do or undergo things (which he refers to as “things”). Hence, there are three basic categories: substance, quality, and action. At the back of Valla’s mind are the grammatical categories of noun, adjective, and verb; but in many places he points out that we cannot assume that, for instance, an adjective always refer to a quality or a verb to an action (Repastinatio, 1:134–156; 425–442; DD 1:240–80). These three categories are the only ones Valla admits; the other Aristotelian categories of accidents such as place, time, relation and quantity can all be reduced to quality or action. Here, too, grammar plays a leading role in Valla’s thought. From a grammatical point of view, qualities such as being a father, being in the classroom, or being six-feet tall all tell us something about how a particular man is qualified; and there is, consequently, no need to preserve the other Aristotelian categories.