1. Socrates: a brave Athenian soldier. He dislikes politics and focuses more on philosophy that uses humans as objects of thought.
2. Plato: one of Socrates's students. The thought used in philosophy is that the knowledge gained from the senses or experience is impermanent or changing, while the knowledge of reason is permanent or unchanging.
3. Aristotle: son of a private physician to the Macedonian king Amyntas. He got empirical knowledge from his father. Discussion of Philosophy by Aristotle include: logic, nature, psychological, biology, metaphysics, ethics, politics and the state.
4. Xenophanes: his name became famous because for the first time he made the assumption that there is a conflict between philosophical thinking with mythical thinking.
5. Pythagoras: the thought of all things is a number and all natural phenomena forget the sensory expression of a mathematical comparison. He revealed that the universe is a harmonious whole like music.
