The Greeks had a general tendency to divide the world into pairs of things, one opposed to the other. They saw everything as divided into two parts, which fought with each other all the time. So they tended to divide people into two groups too. There are a lot of different ways to divide people. And people have rational thought, but animals do not.
People are also divided from gods .
People eat food, and gods do not. People die, but gods do not. Another way of looking at these divisions is to divide Greek people from barbarians , people who are not Greek. The Greeks called all foreigners barbarians, even if they were very civilized like the Egyptians or the Persians . Or you can divide men from women.