Socrates and Plato (one of Socrates’ students), together with Aristotle (a student of Plato), are hailed as the Big Three ancient Greek philosophers. Socrates was born during the golden age of Athens when it was ruled by Pericles, and died as Athens declined. A historical figure of distinctive personality, controversy and legend, he was Plato’s teacher but left behind no written work. His speech and thought can be found in Xenophanes’ works. Accused by aristocrats of corrupting the young, Socrates was executed by being forced to drink a cup of poisonous hemlock. As a teacher, he applied a distinctive approach of inspiration and debate in his teaching. In philosophy, he was the founder of Platonism. Stressing the importance of ethics, he was the first in ancient Greece to propose the pursuit of universal ethics through reason and thinking. In founding moral philosophy, his assertion of reason guided by morality justifies the proposition that virtue equals knowledge, taking knowledge as the root of goodness and ignorance that of wrongdoing. The first to suggest idealist teleology, Socrates assumed that everything was created and arranged by God, which demonstrates God’s wisdom and telos (purpose). With his proposition that “I know that I know nothing,” he thought that people were only smart if they forsook the exploration of nature, which is the realm of the gods, and admit their ignorance. People should obey the gods because they have the most knowledge and are the source of knowledge. In logic, according to Aristotle, Socrates was the one who presented inductive arguments, which identify definite arguments based on particular instances emphasize general definitions, thereby precisely explaining concepts. Socrates’ philosophical thoughts mainly affirm the existence of criteria for what is good or bad.

Plato was the founder of objective realism. Born into an Athenian aristocratic family and well educated, he was enthusiastic about politics as were other aristocrats. After becoming a student of Socrates, he revered the thoughts and character of his teacher. In order to realize his idea of an ideal aristocratic state, after the death of Socrates he traveled to various places, such as Egypt, Asia Minor, and southern Italy in order to undertake political activities. In 387 bc he returned to Athens and established an academy named after Academus, a Greek hero, and taught there for forty years until his death. Plato was a prolific writer, whose main thoughts are manifested in The Republic and The Laws. His Academy was the earliest higher education institution, and it gave its name to future higher scholastic institutions. Besides philosophy, he taught mathematics, astronomy, acoustics, botany, and knowledge of other natural sciences, while philosophy maintained the highest status. The purpose of the Academy was not to impart practical techniques but to focus on theoretical wisdom, with the emphasis on thinking and analysis.

The philosophical system of Platonism is both extensive and profound. From his perspective, the world is composed of the World of Forms and the World of Phenomena. The World of Forms is the real existence of permanence, while the World of Phenomena, which can be felt by human sense organs, is only its faint shadow. Each of these phenomena displays transience and variation owing to the effects of time and space. With this starting point, Plato proposed an epistemology of the Theory of Forms and Recollection, and established this as the philosophical foundation of his teaching theories.

Aristotle is regarded as a universal genius of ancient knowledge. He was born in Stagira; his father was a court physician to the Macedonian king Amyntas and died when Aristotle was very young. Aristotle was sent to Athens aged eighteen, studied in Plato’s Academy, and remained there as a teacher. After the death of Plato, he left Athens for Assos to found an academy for teaching and research. Three years later the Persian Empire took the city, and Aristotle escaped to Mytilene on the island of Lesbos. Returning to Athens in 335 bc, he established a new school near the Lyceum stadium next to the Temple of Apollo; for this reason his school was named Lyceum. Compared with Plato’s Academy, it put more emphasis on practicality, stressed the importance of questioning, and paid attention to material collection, repeated attempts, and exploration.

Aristotle is universally revered in the history of science because, before the Renaissance in modern Europe in terms of scholarship, no one was comparable to him in their systematic investigation and comprehensive mastery of knowledge, though some attained tremendous achievements in specific fields. One of the intellectual tasks of the early Middle Ages was to assimilate Aristotle’s research from incomplete summaries of his works. After his collected works were published, writers of the later Middle Ages made every effort to uncover his original meanings. His works were regarded as the encyclopedia of scholarship in the ancient world. Besides physics and astronomy, he also improved other disciplines that he worked on. In addition, he was the founder of inductive method and the first proponent of organized research. Above all, he is celebrated for his contribution to science and the classification of knowledge. His major works include Categories, De Interpretatione, Prior Analytics, Posterior Analytics, Topics, Sophistical Refutations, under the umbrella title of Organon, mainly dealing with logic; Metaphysics, in which covers general abstract theoretical problems; Physics, On the Heavens, On Generation and Corruption, and On the Soul, expounding subjects related to natural sciences; Nicomachean Ethics and Eudemian Ethics, dealing with ethical topics. He also wrote Politics, Poetics, Rhetoric, and other works on biology and economics.

Augustine, born in Tagaste, a small town in northern Africa that was part of the Roman Empire, now Algeria, synthesized the essence of patristic philosophy. He was converted to Christianity by his mother but became a follower of Manichaeism (a dualistic religious movement) during his studies in the rhetoric school. After graduation, he taught rhetoric and oratory first in Carthage and then in Rome and Milan. Being influenced by Ambrose, the Archbishop of Milan, he broke away from Manichaeism and became immersed in the works of Platonism and skepticism. The turning point of his eventual conversion to Christianity happened when he was reflecting in a garden. According to his autobiography, Confessions, Augustine heard a child’s voice urging him to “take up and read! take up and read!” as he was wondering about his beliefs. He hurriedly opened the Bible that was to hand and found himself facing the teachings of St. Paul: “Let us walk honestly, as in the day; not in rioting and drunkenness, not in chambering and wantonness, not in strife and envying. But put ye on the Lord Jesus Christ, and make not provision for the flesh, to fulfil the lusts thereof.” This struck him like lightning as Augustine had lived a frivolous life in his youth. “By a light as it were of serenity infused into my heart, all the darkness of doubt vanished away.” At Easter in 387 he was baptized by Ambrose and officially converted to Christianity. Later, on his return to his hometown, he was elected a priest of Hippo and promoted to archbishop in 395. During his tenure, Augustine exerted tremendous energy writing, preaching, organizing orders, and refuting pagan beliefs. In his later years he witnessed the invasion of the Vandals, and he died before their occupation of Hippo. After his death, North Africa broke its ties with the Roman Empire and became free of the control of the Roman Church. However, Augustine’s works spread to Europe and became the spiritual treasure of Catholicism and Protestantism. Among his prolific works, which are regarded as a theological encyclopedia, Confessions, On the Trinity, and The City of God are his masterpieces, containing considerable philosophical treatises.

Thomas Aquinas, the most important philosopher in the Middle Ages, was born in Roccasecca, Italy, on the Aquinas family’s manor. As a prestigious Lombardic family, the Aquinases were closely connected with the Church and the Holy Roman Empire. Thomas was sent to the celebrated Monte Cassino Abbey, where he received the necessary training to one day become an abbot, as his parents wished. In 1239, the excommunicated Frederick II sent troops to occupy and close the abbey, forcing Thomas to continue his studies at the University of Naples. There he began to learn Aristotle’s works of metaphysics, natural philosophy, and logic, and joined the Dominican Order. On the recommendation of Albertus Magnus, the influential Dominican scholar, Aquinas attended the seminary at the University of Paris and completed his studies in 1256. He wrote extensively, anything up to about 15 million words. Among his works, those containing philosophical views are On Being and Essence, On the Principles of Nature, On Truth, Commentary on Boethius’ On the Trinity. His masterpieces are Summa Theologica and Summa contra Gentiles. Aquinas wrote commentaries on Aristotle’s works, including Metaphysics, Physics, Posterior Analytics, De Interpretatione, Politics, Ethics, Sense and Sensibilia, On Memory, and On the Soul.

Applying Aristotle’s philosophy to theology, Aquinas created a stupendous scholastic philosophical and theological system; he also made significant contributions to ethics, logic, politics, metaphysics, and epistemology. His famous fivefold proof for the existence of God had a great impact in the future. His philosophical and theological system was authorized by Pope Leo XIII as the official doctrine of Catholicism, called Thomism; it was not only the greatest achievement of scholastic philosophy, but the largest and most comprehensive system of medieval theology.