Adjectives and common nouns are currently assigned the same semantic analysis: both categories are said to denote sets of individuals (type <e,t>). We will show that this assumption is empirically inadequate and we will assume instead that adjectives denote properties (viewed as primitive entities, not as sets of individuals) instantiated in individuals, whereas (number marked) common nouns basically denote sets of individuals. Correlated with this distinction, we will propose the existence of two distinct rules of predication: (i) an entity is a member of a set of entities and (ii) a property is localized in an entity. Our analysis is based on the Aristotelian view that has become the basic postulate of property theory (Chierchia 198...