As Cox points out, "Without inheritance, every class would be a free-standing unit, each developed from the ground up. Different classes would bear no relationship with one another, since the developer of each provides methods in whatever manner he Chooses. Any consistency across classes is the result of discipline on the part of the programmers. Inheritance makes it possible to define new software in the Same way we introduce any concept to a newcomer, by comparing it with something that is already familiar."
p. 56: Booch is citing: Cox, B. 1986. Object-Oriented Programming An Evolutionary Approach. Reading, MA: Addison-Wesley, p. 69. - Object-oriented design: With Applications, (1991)