This paper has two main claims: First, it will argue that most of what is usually interpreted as Plato's ethics is concerned primarily with the establishing a Substantive Theory of the Good. Secondly, it will be shown that Plato's link between his STG and matters of obligation is a very close one, and cannot be analyzed along either utilitarian or Kantian lines.
Moravcsik, Julius M.E., "Ideals and Obligations in Plato's Ethics" (1984). The Society for Ancient Greek Philosophy Newsletter. 114.