As Greek colonists travelled to different areas of the Mediterranean, they met people with completely different beliefs and ideas. Historians think this led them to investigate and study.

Unlike anyone before them, the Greeks looked for common sense answers to their questions. They developed logic and many rules of argument. Argument from probability (asking, "Is it likely?" ) is still used in courts of law today by lawyers. Above all, the Greeks realised that there are two sides to every question: 'Sickness is bad for the patient, but good for the doctor; a worn out shoe is bad for the owner, but good for the cobbler.' The idea of opposites became very important in Greek thought.