The six cases can be organized by possibility and instantiation:
1. External instances are impossible: “the non-possible.”
2. Instances are possible, but none actually exists: “a ruby mountain.”
3. One exists; another is ruled out by a distinct proof: the Necessary Existent.
4. One exists; another is possible: the historical illustration of the sun.
5. Many exist in a finite set: the older example of the wandering planets.
6. Multiplicity is not fixed by a finite pre-set count: humans, horses and sheep.
The cases distinguish external instantiation and modal status. They do not change what it means for a concept to be universal.