TITLE: So that's what its called (or the Liskov Substitution Principle) PROBLEM: osinski@porter.cs.nyu.edu (Ed Osinski) [...] Inheritance is useful where, when you have a value of type pointer or reference to the base class, you don't care which derived class it really points to. RESPONSE: rmartin@rcmcon.com (Robert Martin) You are referring to the Liskov Substitution Principle which states that users of a base class should be able to use derived classes without knowing it. [...]