Is WordPress Object-Oriented? A Thorough Exploration

Here at WPShout, we’ve got some thorough tutorials on using object-orientation as a WordPress developer. We’ve hopefully convincingly explained that it’s pretty common and easy for a developer to write something when programming WordPress that is OO. Many many plugins you see are is essentially object-oriented WordPress plugins. What I want to explore today is a more esoteric question: Is WordPress an object-oriented system? Or, in short “Is WordPress OOP?”