Recall we introduced the concept of inheritance back in chapter 1. There, we motived the idea with a description from real life. Inheritance in that chapter was described as a process of categorization. We categorized objects into different levels, using abstraction to factor out common features. Categories lower in the hierarchy held all the properties known concerning categories higher in the hierarachy. For example, everything you know about an Animal is applicable to a Mammal, and so on.