“Aristotle drew a distinction between essential and accidental properties. The way he put it is that essential properties are those without which a thing wouldn’t be what it is, and accidental properties are those that determine how a thing is, but not what it is. For example, Aristotle thought that rationality was essential to being a human being and, since Socrates was a human being, Socrates’s rationality was essential to his being Socrates. Without the property of rationality, Socrates simply wouldn’t be Socrates. He wouldn’t even be a human being, so how could he be Socrates? On the other hand, Aristotle thought that Socrates’s property of being snub-nosed was merely accidental; snub-nosed was part of how Socrates was, but it wasn’t essential to what or who he was. To put it another way, take away Socrates’s rationality, and he’s no longer Socrates, but give him plastic surgery, and he’s Socrates with a nose job.”