During his lifetime, Jean-Paul Sartre enjoyed unprecedented popularity for a philosopher, due partly to his role as a spokesman for existentialism at the opportune moment, when this set of ideas filled the spiritual gap left amidst the ruins of World War II. Existentialism was a philosophy of action and showed the ultimate freedom of the individual. In Sartre's hands, it became a revolt against European bourgeois values.

One of the two major philosophical traditions of the twentieth century was linguistic analysis, derived largely from Wittgenstein. The other, diametrically opposed, came from Heidegger, and its fundamental question was, "What is the meaning of existence?" For Heidegger, this question could not simply be "analyzed away". It was beyond the reach of logic or reason. It was the primary "given" of every individual life. To confront it, Heidegger needed to develop an entire new form of philosophy.

Aristotle wrote on everything from the shape of seashells to sterility, from speculations on the nature of the soul to meteorology, poetry, art, and even the interpretation of dreams. Apart from mathematics, he transformed every field of knowledge that he touched. Above all, Aristotle is credited with the founding of logic. When he first divided human knowledge into separate categories, he enabled our understanding of the world to develop in a systematic fashion.

Spinoza's brilliant metaphysical system was derived neither from reality nor experience. Starting from basic assumptions, with a series of geometric proofs he built a universe which was also God, one and the same thing, the classic example of pantheism. Although his system seems an oddity today, Spinoza's conclusions are deeply in accord with modern thought, from science (the holistic ethics of today's ecologists) to politics (the idea that the state exists to protect the individual).

With Hegel, philosophy became very difficult indeed. His dialectical method produced the most grandiose metaphysical system known to man. Even Hegel conceded that "only one man understands me, and even he does not." Hegel's system included absolutely everything, but its most vital element was the dialectic of the thesis, antithesis, and synthesis. This method sprang from Hegel's ambition to overcome the deficiencies of logic and ascended toward mind as the ultimate reality.

Rene Descartes spent most of his childhood in solitude, a situation that also came to characterize his adult life. Fortunately, these countless lonely hours helped Descartes produce the declaration that changed all philosophy: "I think, therefore I am." Eventually convincing himself to doubt and disregard sensory knowledge, Descartes found he could prove his existence through his thoughts. This internal information, he believed, was the true reality and external forces were hopelessly deceiving.

With Friedrich Nietzsche, philosophy was dangerous not only for philosophers but for everyone. His ideas presaged a collective madness that had horrific consequences in Europe in the early 1900s. Though his philosophy is more one of aphorisms than a system, it is brilliant, persuasive, and incisive. His major concept is the will to power, which he saw as the basic impulse for all our acts. Christianity he saw as a subtle perversion of this concept, thus Nietzsche's famous pronouncement, "God is dead."

In an age when philosophers had scarcely glimpsed the horizons of the mind, a boy named Aristocles decided to forgo his ambitions as a wrestler. Adopting the nickname Plato, he embarked instead on a life in philosophy. In 387 B.C. he founded the Academy, the world's first university, and taught his students that all we see is not reality but merely a reproduction of the true source. And in his famous Republic he described the politics of "the highest form of state."

Immanuel Kant taught and wrote prolifically about physical geography yet never traveled further than forty miles from his home in Kvnigsberg. How appropriate it is then that in his philosophy he should deny that all knowledge was derived from experience. He insisted that all experience must conform to knowledge. According to Kant, space and time are subjective; along with various "categories," they help us to see the phenomena of the world, though never its true reality.

Just a century after it had begun, philosophy entered its greatest age with the appearance of Socrates, who spent so much of his time talking about philosophy on the streets of Athens that he never got around to writing anything down. His method of aggressive questioning, called dialectic, was the forerunner of logic; he used it to cut through the twaddle of his adversaries and arrive at the truth. Rather than questioning the world, he believed, we would be better off questioning ourselves.

In his landmark best seller The Tipping Point, Malcolm Gladwell redefined how we understand the world around us. Now, in Blink, he revolutionizes the way we understand the world within. Blink is a book about how we think without thinking, about choices that seem to be made in an instant, in the blink of an eye, that actually aren't as simple as they seem. Why are some people brilliant decision makers, while others are consistently inept?

In Mastery, Robert Greene's fifth book, he mines the biographies of great historical figures for clues about gaining control over our own lives and destinies. Picking up where The 48 Laws of Power left off, Greene culls years of research and original interviews to blend historical anecdote and psychological insight, distilling the universal ingredients of the world's masters.

In The Righteous Mind, social psychologist Jonathan Haidt explores the origins of our divisions and points the way forward to mutual understanding. His starting point is moral intuition - the nearly instantaneous perceptions we all have about other people and the things they do. These intuitions feel like self-evident truths, making us righteously certain that those who see things differently are wrong. Haidt shows us how these intuitions differ across cultures, including the cultures of the political left and right.

Durant lucidly describes the philosophical systems of such world-famous “monarchs of the mind” as Plato, Aristotle, Francis Bacon, Spinoza, Kant, Voltaire, and Nietzsche. Along with their ideas, he offers their flesh-and-blood biographies, placing their thoughts within their own time and place and elucidating their influence on our modern intellectual heritage. This book is packed with wisdom and wit.

In SPQR, world-renowned classicist Mary Beard narrates the unprecedented rise of a civilization that even 2,000 years later still shapes many of our most fundamental assumptions about power, citizenship, responsibility, political violence, empire, luxury, and beauty.

In an age when philosophers had scarcely glimpsed the horizons of the mind, a boy named Aristocles decided to forgo his ambitions as a wrestler. Adopting the nickname Plato, he embarked instead on a life in philosophy. In 387 B.C. he founded the Academy, the world's first university, and taught his students that all we see is not reality but merely a reproduction of the true source. And in his famous Republic he described the politics of "the highest form of state."

A handsome recluse, plagued by indecision and hypochondria, Franz Kafka nonetheless exhibited an extraordinary strength. He developed the uncanny ability to observe himself with cool objectivity, and he cultivated this ability in his writing, where it appeared in increasingly original metaphorical form. His works became among the greatest of the twentieth century, and his influence permeated far and wide, transcending literature.

In Rousseau we encounter a walking ego, naked sensibility. Feeling triumphs over intellectual argument in his works, which are both deeply stirring and deeply inconsistent. Yet while his contemporaries Kant and Hume may have been superior academic philosophers, the sheer power of Rousseau's ideas was unequaled in his time. It was he who encouraged the introduction of both liberty and irrationality into the public domain.

Spinoza's brilliant metaphysical system was derived neither from reality nor experience. Starting from basic assumptions, with a series of geometric proofs he built a universe which was also God, one and the same thing, the classic example of pantheism. Although his system seems an oddity today, Spinoza's conclusions are deeply in accord with modern thought, from science (the holistic ethics of today's ecologists) to politics (the idea that the state exists to protect the individual).

We see our age as the greatest in human history, filled with seemingly unending originality. Yet such dynamism is not a necessary characteristic of great eras. Among the most long-lasting and stable civilizations was that of medieval Europe. There stasis was achieved, and with it a stability that permitted the development of structured thought and intellectual embellishment of unparalleled degree.

From a young age, James Joyce showed a precocious and original intellect and a confidence in his own artistic destiny. He would indeed go on to transform the nature of modern literature, employing a unique stream-of-consciousness technique rich in symbolism and wordplay. Through his art, the Dublin native sought to reveal the radiance and meaning that lurks in the everyday world - "the soul of the commonest object" - evoking a heightened sense of consciousness within the grit of common life.

"If we accept Wittgenstein's word for it," Paul Strathern writes, "he is the last philosopher. In his view, philosophy in the traditional sense was finished."

Rene Descartes spent most of his childhood in solitude, a situation that also came to characterize his adult life. Fortunately, these countless lonely hours helped Descartes produce the declaration that changed all philosophy: "I think, therefore I am." Eventually convincing himself to doubt and disregard sensory knowledge, Descartes found he could prove his existence through his thoughts. This internal information, he believed, was the true reality and external forces were hopelessly deceiving.

Karl Marx's devastating critique of capitalism, and his proposal of communism as the answer to the failings of the capitalist system, bore their greatest fruits in the twentieth century with the formation of the communist state in the Soviet Union. This great venture has now all but completely failed. Yet the force of the communist belief offered the prospect of "justice on this earth" to countless numbers. And Marx's critique has influenced generations of thinkers who call themselves Marxists.

One of the two major philosophical traditions of the twentieth century was linguistic analysis, derived largely from Wittgenstein. The other, diametrically opposed, came from Heidegger, and its fundamental question was, "What is the meaning of existence?" For Heidegger, this question could not simply be "analyzed away". It was beyond the reach of logic or reason. It was the primary "given" of every individual life. To confront it, Heidegger needed to develop an entire new form of philosophy.