Plato made the distinction between individual things and their properties a cornerstone of his philosophy. He distinguished between two realms: the realm of changing individual things and the realm of unchanging properties. Plato, by discovering that properties are abstract, discovered that there are things which do not belong to the universe. He discovered that there is a world and not just a universe. Since Plato’s time, there have been philosophers who have claimed that there is nothing else but the universe. They have argued that there is no such thing as the world. The structure of the world, they assert, is the proper subject of study for the philosopher, while the universe is the proper subject of study for the scientist. The discovery of the world immediately invites the question of whether or not there are any other abstract things. Without exemplification, Plato’s world splits into the universe and a realm of properties.