Identity is the relationship that a thing bears only to itselft

If 2 things are the same, they have an identity relation

Indiscernibility of Identicals: If 2 things are the same, they must share all the same properties.

Properties of an object can be of two types...

  • Essential properties: Core elements needed for a thing to be the thing that it is
  • Accidental properties: Properties that can be taken away without making it a different thing

Fungability: Ability of an item to be changed for any other item of the same type. Eg a 1 Euro coin can be replaced by any other 1 Euro coin.