By calling everything into doubt, Descartes laid the foundations of modern philosophy. With the celebrated words "I think therefore I am," his compelling argument swept aside ancient and medieval traditions. He deduced that human beings consist of minds and bodies; that these are totally distinct "substances"; that God exists and that He ensures we can trust the evidence of our senses.

Socrates is in prison, sentenced to die when the sun sets. In this final conversation, he asks what will become of him once he drinks the poison prescribed for his execution. Socrates and his friends examine several arguments designed to prove that the soul is immortal. This quest leads him to the broader topic of the nature of mind and its connection not only to human existence but also to the cosmos itself. What could be a better way to pass the time between now and the sunset?

Socrates is on trial for his life. He is charged with impiety and corrupting young people. He presents his own defense, explaining why he has devoted his life to challenging the most powerful and important people in the Greek world. The reason is that rich and famous politicians, priests, poets, and a host of others pretend to know what is good, true, holy, and beautiful, but when Socrates questions them, they are shown to be foolish rather than wise.

In The Republic, Plato tackles the big issues of the state and the individual: how the state should be ruled, and by whom; and the way the individual should lead his life - and why. The lively quality of the dialogue can be clearly appreciated in this new translation by Tom Griffith.

John Locke and his works - particularly An Essay Concerning Human Understanding - are regularly and rightly presented as foundations for the Age of Enlightenment. His primary epistemological message - that the mind at birth is a blank sheet waiting to be filled by the experiences of the senses - complemented his primary political message: that human beings are free and equal and have the right to envision, create and direct the governments that rule them and the societies within which they live.

The leviathan is the vast unity of the State. But how are unity, peace, and security to be attained? Hobbes’ answer is sovereignty, but the resurgence of interest today in Leviathan is due less to its answers than its methods: Hobbes sees politics as a science capable of the same axiomatic approach as geometry.

A dialogue between Socrates and Meno probes the subject of ethics. Can goodness be taught? If it can, then we should be able to find teachers capable of instructing others about what is good and bad, right and wrong, or just and unjust.

Phaedrus lures Socrates outside the walls of Athens, where he seldom goes, by promising to share a new work by his friend and mentor, Lysias, a famous writer of speeches. This dialogue provides a powerful example of the dialectical writing that Plato uses to manifest ideas that are essential to human existence and to living a good life. Phaedrus shows how oral and written forms of language relate to each other and to philosophy.

The dramatic nature of Plato's dialogues is delightfully evident in Symposium. The marriage between character and thought bursts forth as the guests gather at Agathon's house to celebrate the success of his first tragedy. With wit and insight, they all present their ideas about love - from Erixymachus' scientific naturalism to Aristophanes' comic fantasy. The unexpected arrival of Alcibiades breaks the spell cast by Diotima's ethereal climb up the staircase of love to beauty itself.

Kant published this work in 1795, during the aftermath of the American Revolution and the French Revolution. The high hopes of the European Enlightenment had been dampened by the Reign of Terror in which tens of thousands of people died, and the perpetual cycle of war and temporary armistice seemed to be inescapable. Kant's essay is best known as an early articulation of the idea of a league of nations that could bring an end to all hostilities. Today, the United Nations continues to pursue that dream, but lasting peace still seems to be wishful thinking.

Gorgias of Leontini, a famous teacher of rhetoric, has come to Athens to recruit students, promising to teach them how to become leaders in politics and business. A group has gathered at Callicles' house to hear Gorgias demonstrate the power of his art. This dialogue blends comic and serious discussion of the best life, providing a penetrating examination of ethics.

Laches, a general in the Athenian army, saw Socrates fight bravely in the battle of Delium. When he and Nicias, another general, are asked to explain the idea of courage, they are at a loss, and words fail them. How does courage differ from thoughtless and reckless audacity? Can a lion be said to be courageous? What about small children who have little idea of the dangers they face? Should we call people courageous who do not know whether their bravery will produce good or bad consequences?

Hippias of Elis travels throughout the Greek world practicing and teaching the art of making beautiful speeches. On a rare visit to Athens, he meets Socrates, who questions him about the nature of his art. Socrates is especially curious about how Hippias would define beauty. They agree that beauty makes all beautiful things beautiful, but when Socrates presses him to say precisely what he means, Hippias is unable to deliver such a definition.

Socrates questions Ion, an actor who just won a major prize, about his ability to interpret the epic poetry of Homer. How does an actor, a poet, or any other artist create? Is it by knowing? Is it by inspiration? As the dialogue proceeds, the nature of human creativity emerges as a mysterious process and an unsolved puzzle.

Aristotle's Poetics is best known for its definitions and analyses of tragedy and comedy, but it also applies to truth and beauty as they are manifested in the other arts. In our age, when the natural and social sciences have dominated the quest for truth, it is helpful to consider why Aristotle claimed poetry is more philosophical and more significant than history. Like so many other works by Aristotle, the Poetics has dominated the way we have thought about all forms of dramatic performance in Europe and America ever since.