mydog = Dog.new yourdog = Dog.new At the moment, these two dogs have no names. So the next thing I do is call the set_name method to give them names: mydog.set_name( 'Fido' ) yourdog.set_name( 'Bonzo' ) Having given each dog a name, I need to have some way to find out its name later on. How shall I do this? I can’t poke about inside an object to get at the @name variable, since the internal details of each object are known only to the object itself. This is a fundamental principle of ‘pure’ object orientation: the data inside each object is private. There are precisely defined ways into each object (for example, the method set_name) and precisely defined ways out. Only the object itself can mess around with its internal state. The outside world cannot. This is called ‘data hiding’ and it is part of the principle of ‘encapsulation’.