The three pillars of Object Orientation

All object oriented languages, systems, designs and thinking are supported by three pillars:

1. Objects are responsible for their own behaviour.
2. Objects communicate via messages.
3. Objects are specialised.

These three are common to all object oriented systems of whatever kind.

I'm going to describe these in more detail and also explore some of the things that people tend to see as defining qualities of object orientation. What I'm not going to do though is give any examples of languages in any way. The reason is that I want to focus on the principles involved and not get bogged down in discussions about how to see the structure and features of differing languages.