In The Republic it is shown that the true philosopher seeks to know the essential nature of each thing. He is not concerned to know, for example, a multiplicity of beautiful things, but rather to discern the essence of beauty and the essence of goodness, which are embodied in varying degrees in particular beautiful things or particular good things. Non philosophers, who are taken up with the multiplicity of appearances that they do not attend to the essential nature and cannot distinguish, Eg. the essence of beauty from the many beautiful phenomena, are represented as having only opinion and as lacking in scientific knowledge. ... In The Republic... Good is... compared to the sun, the light of which makes the objects of nature visible to all and so is, in a sense, the source of their worth and value and beauty. This comparison is, of course, but a comparison, and such should not be pressed: we are not to suppose that the Good exists as an object among other objects. On the other hand, as Plato clearly asserts that the Good gives being to the objects of knowledge and so is, as it were, the unifying and all comprehensive Principle of the essential order, while itself excelling even essential being in dignity and power, it is impossible to conclude that the Good is a mere concept or even a non existent end, a teleological principle, as yet unreal, towards which all things are working: it is not only an epistemological principle, but also - in some ill defined sense - an ontological principle, a principle of being. It is therefore, real in itself and subsistent. It would seem that the Idea of the Good of The Republic must be regarded as identical with the essential Beauty of The Symposium. Both are represented as the high peak of an intellectual assent... The Idea of the Good gives being to the Forms or essences of the intellectual order, while science and the and the wide ocean of intellectual beauty is a stage on the assent to the essentially beautiful. Plato is clearly working towards the conception of the Absolute, the absolutely perfect and exemplary pattern of all things, the ultimate ontological Principle. This Absolute is immanent, for phenomena embody it, "copy" it, partake in it, manifest in it, in their varying degrees; but it is also transcendent, for it is said to transcend even being itself, while the metaphors of participation and imitation imply a distinction between participation and the partaken of... Any attempt to reduce the Platonic Good to a mere logical principle necessarily leads to a denial of the sublimity of the Platonic metaphysic... [and] to the conclusion that the... Neo Platonist philosophers entirely misunderstood the essential meaning of the Master.Plato's theory of the forms is complex and fascinating in many ways. One of the most common criticisms of it is on the question of how the ideal and the real interact. Plato was aware of this and in one of his dialogues he uses a speaker named Paramenides to voice the confusion that results when the relationship between the physical and the transcendent is treated as being of the same nature as the relation between two physical objects. If the two kinds of object are really distinct, however, a new problem emerges. If we have only sensory knowledge of physical objects, how can we ever know anything at all about a transcendent object? As Copelston puts it,
If the two worlds are merely parallel, then, just as we would know the sensible without being able to know the Ideal World, so a divine intelligence would know the Ideal World without being able to know the sensible world.If the worlds are not parallel, then they must intersect in some way. But how? How can something be One and many at the same time? The Neo Platonists suggested that the Ideal Forms were the thoughts of God, who is the Absolute. The world is thus a unity as contained in the Divine Mind and a plurality when realized in Nature. There is some debate as to whether Plato was heading in the direction of monotheism. If in fact he was, I find it extraordinary that the ancient Jews beat this pillar of western thought to it by thousands of years. Practically speaking, Plato is far too quick to resort to force regarding his understanding of the Good. In The Republic and even in The Laws, which came much later in his life, he tightly regulates almost all aspects of life in the City. That there is a manifest difference between an action that is forced and one that is done freely seems to slip by him. That the force in question is motivated by knowledge of an objective good does not alter the equation at all. Like Rousseau, he has no doubt that "men must be forced to be free," although Plato's phrase would probably have been the even more improbable sounding "men must be forced to be happy." There is more muddying of the waters as well. Even if there are objective goods that we can know - with this I agree - it does not follow that we will know how to respond to that knowledge. That is a life's work for any individual, so how can an individual hope to tell others how they "must" respond to the Good? The ancients simply did not think like that and I suppose we can consider the huge jump forward that Plato represents over earlier philosophy to be a laurel that few of us will ever be so lucky as to reap. The distinctions between is and ought and church and state are distinctions that would not become commonplace until much later. Generally speaking, questions about what is are the realm of science and of the state. Ought is a question for the churches, who can direct us towards the high peaks of the Good without compulsion. Critically, however, we moderns fail to grasp that the small platoons (to use Burke's phrase) of the family and the church come first. We have to know what we want to do, and ought to do, before they can be done. What are we? What is the state? What should be the object of scientific study? What kind of study is scientific? Those are all religious questions. Our little platoons come together to work out how we will bring forward our ideas and that discussion happens not just in the halls of parliament, but in every living room and shop floor. If we do not construe the relationship in this way, then the state will become the church again, as it was for Plato. That would be a step backwards, threatening all of us, even those with their hands on the tiller at the moment. The moment is a fleeting thing. In terms of Plato's distinction between opinion and science, I would add that each of us has only an opinion of the Good, but when we engage in discussion with others - past and present! - then we can begin to see the kinds of commonalities that allow us begin to speak of the Good as an objective entity.