The Cambridge Companion to Plato

In the Parmenides, there is a complex treatment of the relationship between Unity and such other Forms as Sameness and Difference, Motion and Rest, Limited and Unlimited.

What we must strive for in our souls and as members of a political order – the unification of diverse elements into a harmonious whole – is something that the Forms already possess by their very nature.

The Forms are not a mere aggregate of abstract objects, but are in some way connected to each other: They form an ordered kosmos (500c) and therefore each must be studied not in isolation from others but as a member of a unified whole.

A good political community, Plato assumes, must be one that promotes the well-being of all the citizens; and if the citizens fail to understand where their own good lies, then it is the proper task of political leaders to educate them.

Forms are not in turn dependent for their names on anything else.

So, when Plato says that Forms are completely real, he means that they are at the top of a scale that ranks objects according to their degree of ontological dependency

When we point to the carpenter’s creation and call it a bed, our assertion is acceptable only if it is construed in the right way.

When we point to an image in a painting and call it a bed, what we say is in a way correct, if our claim is taken in the right way. What makes it something that is properly called a bed is its having the right relationship to the functional bed

It is this same relationship of dependency that he thinks exists between the visible bed of the carpenter and the Form.

in saying that the painter’s image of a bed is not a true bed, he is not expressing doubts about the existence of the painting; rather, he is trying to express the point that the painter’s image is in some way derivative from or dependent on the functional object he is representing.