Plato advocated for the goods of excellence, but defining those goods and what they looked like in practice was a job he left unfinished. It was his student Aristotle who was to complete Plato’s project and give the goods of excellence there classic articulation.
MacIntyre summarizes his work thus far,
Two dominant images of human life emerge from post-Homeric reflection. Both are images of aiming and striving. According to the one human beings aim at excellence. Some may misconceive what excellence is, and may fall short of attaining that at which they aim. But all, whatever their degree of achievement, are measured by a standard which they did not make but which they discover…
A second rival image is that according to which human beings aim at a particular kind of power, the power of remaking the social and natural world, so far as possible, into conformity with one’s own desires (88).
The great corrective that Aristotle gives to Plato’s project is to connect the world of forms to the actual world. For Plato, it seemed as if there was no way to get from the world of the cave to the formal world of universal knowledge (epistemé) outside through practical knowledge or experience (phrônésis). Aristotle holds that through practical experience we can arrive at universal knowledge through a process of induction (epagôgé). We reason from the particulars to a universal, in the quest for justice we reason from the various constitutions of numerous city-states to the best and universal understanding of justice of which they are defective examples, just as we are able to refine the crude oil that comes out of the ground into the pure product that will run our cars.
This quest for universal knowledge (epistemé) is a dialectical process one in which through reflection on practical experience we arrive closer and closer to true universal knowledge or first-principles which explain the whither and wherefore of the goods of excellence and enable us to adjudicate between which human actions will help or hinder our pursuit of them. The dialectical discovery of first-princples looks like a process of hypothesis and verification. True universal knowledge are the propositions which can account for all of our current practical knowledge without being altered or refuted by other experiences.
Another difference between Plato and Aristotle – or at least one reading of Plato and Aristotle – was the necessity of the polis for forming virtue. This can be traced to the different understandings that each had on the role of practical and universal knowledge. Since Plato posits a radical disconnect between the two he can be plausibly held as arguing that the virtue of the individual precedes and is independent from that of the polis. Various moral philosophers have picked up on this aspect of the Platonic tradition and held that because of the disconnect between practical and universal knowledge, each individual voice must be given priority in determining what the best course of action is for them, irrespective of experience.
But for Aristotle, the structure of the polis itself was the necessary context for the formation of individual virtue. Since universal knowledge requires practical knowledge, and practical knowledge requires social interaction, the polis is the indispensable school of virtue. Hence, those not schooled the polis can lay no claim to understanding the goods of excellence because they have no practical knowledge. Priority in following a course of action in pursuit of various goods is to be given to those well-schooled in political virtues. Ethics is a branch of politics.
The search for goods of excellence is thus a communal and political enterprise, as opposed to an individual one. This cleavage between the pursuit of the good as communal vs. individual is one of the enduring divides within the debates over the demands of justice and practical rationality, between a libertarian conception of freedom and one whose sees true freedom as the ability to pursue the goods of excellence as they are universally understood.