Theory of Forms
Plato's Theory of Forms provides Plato's explanation of the nature of Reality. In it, Plato upholds the distinction between what is most Real and sensibility, the world of the five senses. In the Platonic view, the world that we experience as changing is a world of Becoming. It should not be taken, however, that the world of sense has no connection with the Forms [ιδέες].
The Forms, also understood as the Platonic Ideas, reside at the top of the hierarchy of Platonic Reality. The Forms of Being are only surpassed by the Good, a reality beyond Being. In this sense, Being is already a step lower than the Good in the Platonic ladder of truth although much higher than what can be found in the sensible world of change. For our purpose, it is helpful to think of Being in relation to Becoming. External causes can effect changes and move sense objects but without external causes, in the Platonic view, objects will lack motion. As such, they do not exist 'in themselves' and are not self-moving, as Plato believes, in the case of the soul. The Forms exist in themselves, and need nothing further to complete themselves. Examples of Platonic Ideas (Forms) are Justice, Love, Virtue and Courage. These Forms correspond, respectively, to the gods Dikē [Δίκη], Eros [Ἔρως], Virtue [ἀρετή], and Courage [ανδρεία].
For Plato, the Forms are not mere abstractions or mental constructions and should not to be equated to 'thoughts'. Such a way of thinking belongs to a later period of philosophy that distinguishes between inner and outer 'substances'. A Platonic Form is outside of and beyond any mind, especially a sensible mind. In Plato, and in Greek tragedy, e.g., Sophocles, and from the standpoint of an archaic Greek sensibility generally, truth is still an external Being that works upon human affairs. Truth has not yet internalized itself to the form of rational essences: thought. in other words, truth is not conceived as abstractions of the mind. For Plato, the Forms are real Beings. In Phaedrus, Plato refers to them as personifications of the gods themselves whose reality we can recollect and therefore connect with through anamnesis. In the Myth of the Charioteer of the same dialogue, Socrates explains the hierarchy of these beings and shows, in conjunction to them, the manner in which a man might be given or be intrinsically linked to a particular god. It might appear paradoxical that Socrates both rejects and uses myth in the dialogues, that his argument often relies on myth for its logos [truth]. However, if, as he believes, the Good is unreachable and beyond Being, and if the Forms are themselves beyond sensible experience, a sort of image-making that helps the hearer recollect immaterial reality is acceptable as a pathway of understanding what the forms might be, of approaching ultimate reality.
To make sense of the previous, it is well to remember that, for Plato, every physical object can be thought to have a connection with a Form. In Platonic philosophy, this means that physical objects, and even discourse itself, are images, copies of the fundamental reality beyond sensibility. These copies can be better or worse. They can more closely resemble the real in which they participate - ultimate reality - a state of affair to which Plato would not object to, or, they can be bad copies (simulacra). As images of reality move further away from actual reality (the Forms), however, their participation in the Forms decreases, and they become mere shadows of reality, having little of the stuff of the Forms (reality) left in them.
In Plato's conception of the way in which material reality participates in Forms, it might first appear that matter and Form are completely separate, therefore placing Plato further away from Aristotle's view of substance [form]. However, there is a way that it can be said that, for Plato, matter, because it participates in the Forms, derives its reality from them. Although sensible objects and the eternal Forms are distinct, objects of sense maintains a real connection to the Forms and thereby are able to participate, through them, in real Being. The closer the connection between original and copy, the more reality can be said is to reside in a thing. On this thesis, objects (thoughts, physical things, etc.) can contain less or more reality. However, because sensible objects are only images of the real, the question of discourse and its truth mean that further investigation of the relation of these images - and of image-making in art or discourse or poetry - will have to be carried out to determine the relationship of images to the original from which they obtain their reality: the Forms.
In Book X of the Republic, Plato argued for a hierarchy of images using the example of the image of a bed. At the top of the hierarchy was that which gives the bed its essence, the Form. Thus, the highest image of the bed would be the idea of the bed that was made by God. The second kind of copy [image] was an actual bed (according to our definition of 'actual') made by a carpenter. The third bed was the image of a bed made by a painter. Image-making was not reserved to the painter, however. We learned in the Phaedrus that discourse itself involves a kind of image-making which can, under certain conditions, be viewed as the highest art (Phaedrus, 262e).