Object-oriented programming languages all involve the notions of class and object. We extend the notion of class so that any Boolean combination of classes is also a class. Boolean classes allow greater precision and conciseness in naming the class of objects governed by a particular method. A class can be viewed as a predicate which is either true or false of any given object. Unlike predicates however classes have an inheritance hierarchy which is known at compile time. Boolean classes extend the notion of class, making classes more like predicates, while preserving the compile time computable inheritance hierarchy.
