1) In anthropology, Plato was the first of the great dualists. He emphasized the sharp distinction between a physical man and the real eternal man.
2) In metaphysics, Plato is remembered for his clear statement of the realist position on universals. A concept such as "justice" or "beauty" is not merely a notion inside someone's mind, nor is it merely a resemblance between the different acts we call just, the different objects we consider beautiful;, etc. It is more than that. The Idea or Form of Justice is a reality, one of the supreme realities, and specific examples are real by virtue of their participation in their universals, not vice versa.
3. In epistemology, Plato believed in critical rationalism. The way to approach truth is to begin with someone's naïve notions and cross-examine them ruthlessly. A philosopher thus becomes a midwife to a truth that will come out of others. (Those unlucky enough to run into him in the agora).
4. In ethics, Plato believed that virtue is a form of knowledge and, accordingly, can be taught. Sometimes he also believed the opposite of this.
5. In politics, Plato believed that a good society will come about only when philosophers become kings, or kings become philosophers.
6. In aesthetics, Plato believed that poets are a lot of trouble, and philosopher-kings would chase them out of a well-designed city