Plato sees the Good as the ultimate form of being. In his book, The Republic, he goes into great detail about what exactly the Good is, as well as making analogies to build upon his theory of the metaphysical form of knowledge that everyone desires to achieve, which will allow them to reach the Good. He holds achieving the Good as a sort of nirvana, which all philosopher-kings, among anyone else, want to achieve. In Plato's eyes, the form of the Good is the highest state of knowledge and understanding that any human being can obtain so in doing so a philosopher-king would rule in virtually the best possible way. In theory, the Good would then be reflected in the city because of the superlative ruling of the king.
In The Republic, Plato's idea of Good being the source of everything that's beautiful, truthful, and just, appears after the example of the prisoner in the cave.
In the world of knowledge, the essential idea of the good is the limit of what can be seen, and can barely be perceived; but, when perceived, we cannot help concluding that it is in every case the source of all that is right and beautiful, in the visible world giving birth to light and its master, and in the intelligible world, as master, providing truth and mind..
In this example, it's explained that there are four levels of human knowledge that are split in two realms, the physical and the intelligible. The sun is what illuminates the physical realm allowing us too see and understand our surroundings, the Good is what illuminates the intelligible realm allowing us to understand and be knowledgeable. Plato makes many comparisons between the sun and the Good and their roles in each realm. The sun is responsible for allowing us to see, just as the Good is respon ...