The problem of universals – how can one thing in general be many things in particular – was solved by presuming that Form was a distinct singular thing but caused plural representations of itself in particular objects.
For example, in the dialogue Parmenides, Socrates states: "Nor, again, if a person were to show that all is one by partaking of one, and at the same time many by partaking of many, would that be very astonishing.
It is neither eternal in the sense of existing forever, nor mortal, of limited duration. The Forms are perfect and unchanging representations of objects and qualities.
For example, the Form of beauty or the Form of a triangle.
For the form of a triangle say there is a triangle drawn on a blackboard. The triangle as it is on the blackboard is far from perfect.
However, it is only the intelligibility of the Form "triangle" that allows us to know the drawing on the chalkboard is a triangle, and the Form "triangle" is perfect and unchanging.
These Forms are the essences of various objects: they are that without which a thing would not be the kind of thing it is.
For example, there are countless tables in the world but the Form of tableness is at the core; it is the essence of all of them.
Plato's Socrates held that the world of Forms is transcendent to our own world (the world of substances) and also is the essential basis of reality.
Super-ordinate to matter, Forms are the most pure of all things.