In ancient Greece, philosophers contemplated and theorized about many different ideas such as human nature, ethics, and moral dilemmas. Ancient Greek philosophers can be categorized into three groups: the Pre-Socratics, the Socratics, and the Post-Socratics.

Pre-Socratic philosophers mostly investigated natural phenomena. They believed that humans originated from a single substance, which could be water, air, or an unlimited substance called “apeiron.” One well-known philosopher from this group was Pythagoras, the mathematician who created the Pythagorean Theorem.

The Socratic philosophers in ancient Greece were Socrates, Plato, and Aristotle. These are some of the most well-known of all Greek philosophers. Socrates (470/469–399 B.C.E.) is remembered for his teaching methods and for asking thought-provoking questions. Instead of lecturing his students, he asked them difficult questions in order to challenge their underlying assumptions—a method still used in modern-day law schools. Because Socrates wrote little about his life or work, much of what we know comes from his student Plato.

Plato (428/427–348/347 B.C.E.) studied ethics, virtue, justice, and other ideas relating to human behavior. Following in Socrates’ footsteps, he became a teacher and inspired the work of the next great Greek philosopher, Aristotle. Aristotle (384–322 B.C.E.), while also interested in ethics, studied different sciences like physics, biology, and astronomy. He is often credited with developing the study of logic, as well as the foundation for modern-day zoology.

The Post-Socratic philosophers established four schools of philosophy: Cynicism, Skepticism, Epicureanism, and Stoicism. The Post-Socratic philosophers focused their attention on the individual rather than on communal issues such as politics. For example, stoicism sought to understand and cultivate a certain way of life, based on one’s virtues, or wisdom, courage, justice, and temperance. Modern philosophers and educators still employ the patterns of thinking and exploration established by ancient Greek philosophers, such as the application of logic to questions of thought and engaging in debate to better convey philosophical ideas.