Theory of Forms
Plato upholds a philosophy that distinguishes ultimate Reality, what is most Real, from the reality of material existence or sensibility. From the Platonic perspective, the world of sensation is a world of phantasms. From this it should not be taken, however, that the world of experience and sense, the world we are most familiar with that opposes the domain of Forms and Reality, has no connection with the Forms.
The Forms, also understood as the Platonic Ideas [eide] reside at the top of the hierarchy of Platonic Reality as forms of Being that are only surpassed by the Good, a reality beyond Being which cannot be conceived. It is helpful to think of Being in relation to material beings. External causes can effect changes and move material beings but without external causes, the material beings have no motion, they do not exist as such and in themselves. The Forms, on the other hand, exist in themselves, needing nothing to complete themselves. Examples of these Platonic Ideas or Forms would be Justice, Love, and Courage.
For Plato, the Forms are not mere abstractions or mental constructions. Such a way of thinking of the non-material beings belongs to a later period of Philosophy. For Plato, the Forms are real Beings, personifications of the gods themselves. In the Myth of the Charioteer (Phaedrus), Socrates explains the hierarchy of these beings and shows, in conjunction to them, the manner in which men are intrinsically linked to one god as opposed to another. This reading is paradoxical given that Socrates rejects myth-making and yet persists in image-making of his own that relies on myth for its logos [truth].
Every physical object can be thought to have a connection with a Form. In Platonic philosophy, this means that physical objects are images, copies of the fundamental reality beyond sensibility. These copies can be better or worse. They can more closely resemble the real from which they participate in ultimate reality or they can be bad copies. As the images of reality move further away from the reality of the forms they become mere shadows, having very little of the substance of the Forms in them.
Because material existence participates in reality, it means that although at first it would appear that matter and form are completely separate in Plato, therefore placing Plato further away from Aristotle's view of substance [form], there is a way in which matter participates in the forms and derives its reality from them. The closer this connection between Original and the Copy, the more reality that can be found in a thing.
In Book X of the Republic, Plato explains the hierarchy of images using the image of a bed. At the top would be that which gives the bed its essence, the Form. The highest image of the bed is the idea of the bed made by God. The second kind of copy is an actual bed made by a carpenter. The third bed is the image of a bed made by a painter. Image-making is not reserved to the painter however, since we learn in the Phaedrus that discourse involves a kind of image-making.