His philosophy can be represented by the following three important points.

1. Knowing that one does not know This idea was the starting point of all his inquiry. At the time, Athens was filled with wise teachers called sophists, who sold knowledge and led people to believe they already understood. Socrates, however, saw that they did not understand the essence of goodness or justice. He taught that the awareness, “I know that I know nothing,” and therefore the pursuit of truth, is the first step toward true wisdom. This humble and objective stance became the foundation of all his thinking.

2. The Socratic method, or maieutics This was the art of dialogue Socrates developed to lead people toward truth. He did not force knowledge into others. Instead, he spoke with citizens in the streets and repeatedly asked questions such as “What is justice?” and “What is courage?” By asking questions that exposed contradictions in their answers, he helped people recognize their own ignorance and encouraged them to bring forth true wisdom for themselves. This process, named after his mother's profession as a midwife, is highly valued as an origin of modern coaching and active learning.

3. The pursuit of living well Socrates valued making the soul as excellent as possible, or living well, above merely earning money or gaining status. He believed that human virtue, or arete, means that the soul possesses correct wisdom, and that people can act rightly only when they truly understand what is right, or good. In other words, knowledge and action cannot be separated; to know something should transform the way one lives.

Yet this relentless dialogue wounded the pride of many powerful people and citizens, creating resentment. As a result, Socrates was sentenced to death on the unreasonable charges of not believing in the gods of the state and corrupting the youth. Although he had the chance to escape prison and survive, he chose to obey the laws of the state, even if unjust, and proved his philosophy and justice by calmly drinking the hemlock and accepting death.

Socrates acknowledged his own ignorance, sought truth through dialogue, and risked his life to keep his soul beautiful. The attitude of continuing to ask questions that he left behind remains an origin of thought to which humanity should return across the ages.

His vast learning can be represented by the following three important points.

1. Realism and emphasis on observation: form and matter Where his teacher Plato pursued the invisible ideal world of Forms, Aristotle emphasized thorough observation of the visible real world. He understood all substances as combinations of matter, the material, and form, which gives things their shape and qualities. For example, wood as matter becomes a desk when it takes on the form of a desk. His refusal to flee into ideals and his commitment to classifying and analyzing the reality before him are why he is called a father of modern natural science.

2. The highest good and the virtue of the golden mean Aristotle believed that the final purpose of every human action is happiness, or eudaimonia, and that this is the highest good. To become happy, one must possess virtue, or arete, and at its core is the golden mean. The mean is the appropriate state without excess or deficiency. Courage, for example, is virtue because it is neither cowardice, a deficiency, nor recklessness, an excess. Temperance is virtue because it is neither indulgence nor rigidity. He saw maintaining balance as the wisdom of living well.

3. The human being as a political animal Aristotle believed that humans cannot live in isolation and can realize their nature only by engaging with others in a community, or polis. Cultivating justice and friendship, or philia, within society is directly connected to human happiness. He also compared and analyzed forms of government such as monarchy, aristocracy, and democracy, realistically asking which political system could make citizens happiest. This thought became a starting point for modern political science and sociology.

In his later years, Aristotle was caught up in political turmoil and forced to leave Athens, but the school he founded, the Lyceum, and the research produced there were passed on to the medieval Islamic world and Europe, becoming part of the world's intellectual heritage.

Aristotle did not remain within abstract idealism; he observed nature, human beings, and society as they are and systematized them. The logical approach to organizing the world that he left behind still lives deeply within the thinking processes of people today.

His philosophy can be represented by the following three important points.

1. The theory of Forms: the origin of idealism This is the core of Plato's philosophy. He believed that the world we grasp through bodily senses, by seeing and touching, is only an imperfect shadow that is constantly changing. He argued that the perfect essence of things, true reality, exists in another realm beyond time and space, and called this the Forms. For example, the various triangles we see in reality are imperfect, but in our minds there is the perfect Form of the triangle. The pursuit of this invisible absolute ideal is the starting point of his philosophy.

2. The allegory of the cave and recollection of the soul To explain the theory of Forms, Plato used the famous allegory of the cave. Human beings, he says, are like prisoners bound facing the wall of a cave, mistaking the shadows cast by a fire behind them for reality. Philosophy is the process of being freed from those bonds, turning around, and seeing the true sun outside the cave, the Form of the Good. He also taught that the human soul originally belonged to the world of Forms but forgot it upon taking on a body, and that seeing beautiful things in this world allows the soul to remember, or recollect, the Forms it once saw.

3. Philosopher-kings and the ideal state Deeply shocked that his teacher Socrates had been sentenced to death by mob rule, a democracy swayed by popular emotion, Plato reflected deeply on the nature of politics. In The Republic, he compared the state to the human soul and envisioned an ideal condition in which the three virtues of wisdom, courage, and temperance, corresponding to rulers, guardians, and producers, are harmonized. He argued that only philosophers who recognize the Form of the Good, those with wisdom, can guide the state correctly and therefore should govern.

Throughout his life, Plato continued to pursue the eternal ideals of truth, goodness, and beauty, without being swept away by the muddy changes of real politics and society.

As the British philosopher Whitehead said, “the history of Western philosophy is only a vast series of footnotes to Plato.” The themes Plato presented, such as the soul, ideals, and the state, still shape our thinking today in changing forms.