Every biography is a story of adventure. The energetic personalities of the world represent an adventure in living. The philosophical personalities, on the other hand, represent an adventure in thinking. And when we examine the lives of the philosophers, we find that the procession of a man's thoughts can be as exciting a spectacle as the pageantry of a man's deeds.

The great thinkers introduced in this work include: Plato, Socrates, Aristotle, Epicurus, Marcus Aurelius, Aquinas, Francis Bacon, Descartes, Spinoza, Locke, Hume, Voltaire, Kant, Hegel, Schopenhauer, Emerson, Spencer, Nietzsche, William James, Bergson, and Santayana.