Immanuel Kant’s Critique of Pure Reason can lay claim to being the most important single work of modern philosophy, a work whose methodology, if not necessarily always its conclusions, has had a profound influence on almost all subsequent philosophical discourse. In this work Kant addresses, in a groundbreaking elucidation of the nature of reason, the age-old question of philosophy: “How do we know what we know?” and the limits of what it is that we can know with certainty.

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.

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.

A landmark in the history of thought, Rene Descartes' Meditations helped bring critical thinking and skepticism to the Western world. Modern philosophers are still captivated by Descartes' radical and controversial departure from his previous beliefs, which has both inspired reverence and provoked anger.

Rene Descartes is often described as the first modern philosopher, but much of the content of his Meditations on First Philosophy can be found in the medieval period that had already existed for more than a thousand years. Does God exist? If so, what is his nature? Is the human soul immortal? How does it differ from the body? What role do sense experience and pure reason play in knowing?

From the perspective of an unbeliever, Fear and Trembling explores the paradox of faith, the nature of Christianity, and the complexity of human emotion. Kierkegaard examines the biblical story of Abraham, who was instructed to sacrifice his son Isaac, and forces us to consider Abraham's state of mind. What drove Abraham, and what made him carry out such an absurd and extreme request from God? Kierkegaard argues that Abraham's agreement to sacrifice Isaac, and his suspension of reason, elevated him to the highest level of faith.

Perhaps one of the most revolutionary works of philosophy ever presented, The Phenomenology of Spirit is Hegel's 1807 work that is in numerous ways extraordinary. A myriad of topics are discussed, and explained in such a harmoniously complex way that the method has been termed Hegelian dialectic. Ultimately, the work as a whole is a remarkable study of the mind's growth from its direct awareness to scientific philosophy, proving to be a difficult yet highly influential and enduring work.

Intended to be a defense of the Christian religion, Pensées is a penetrating collection of thoughts on faith, reason, and theology. Unfinished at the time of Pascal's death, the book consists of philosophical fragments on the "wretchedness" of man and the controversial schisms of the church at the time. It includes the philosopher's infamous wager encouraging belief over agnosticism, as well as his thoughts on numerous other topics. Endlessly quotable, Pensées overflows with pearls of wisdom, each elusive sentence pregnant with a universe of thought.

Perhaps the most influential science book ever written, On the Origin of Species has continued to fascinate for more than a century after its initial publication. Its controversial theory that populations evolve and adapt through a process known as natural selection led to heated scientific, philosophical, and religious debate, revolutionizing every discipline in its wake. With its clear, concise, and surprisingly enjoyable prose, On the Origin of Species is both captivating and edifying.

Published in 1748, An Enquiry Concerning Human Understanding is Scottish empiricist philosopher David Hume's distillation of his mature philosophy. Addressing themes including the limits of human understanding, the compatibility of free will with determinism, weaknesses in the foundations of religion, and the appeal of skepticism, An Enquiry Concerning Human Understanding is Hume's attempt to revise and clarify the ideas of his earlier A Treatise of Human Nature.

Continuing where Thus Spoke Zarathustra left off, Nietzsche's controversial work Beyond Good and Evil is one of the most influential philosophical texts of the 19th century and one of the most controversial works of ideology ever written. Attacking the notion of morality as nothing more than institutionalised weakness, Nietzsche criticises past philosophers for their unquestioning acceptance of moral precepts. Nietzsche tried to formulate what he called "the philosophy of the future".

Dedicated as few men have been to the life of reason, Bertrand Russell has always been concerned with the basic questions to which religion also addresses itself - questions about man’s place in the universe and the nature of the good life, questions that involve life after death, morality, freedom, education, and sexual ethics. He brings to his treatment of these questions the same courage, scrupulous logic, and lofty wisdom for which his other work as philosopher, writer, and teacher has been famous.

The Summa Theologica, by Thomas Aquinas, is a fundamental text in Catholic doctrine, a compendium of theology that has been studied and debated since its first publication in the 13th century. Furthermore, it has been widely regarded as one of the classics of Western philosophy, not least because, perhaps for the first time in such a systematic manner, it set out to consider the views of non-Christian figures such as Aristotle, Boethius, Muslim writers including Averroes (Ibn Rushd) and Avicenna (Ibn Sina) and the Sephardic Jewish scholar Maimonides.

Brought up in the household of a powerful Baron, Candide is an open-minded young man whose tutor, Pangloss, has instilled in him the belief that 'all is for the best'. But when his love for the baron's rosy-cheeked daughter is discovered, Candide is cast out to make his own way in the world. And so he and his various companions begin a breathless tour of Europe, South America and Asia, as an outrageous series of disasters befall them - earthquakes, syphilis, a brush with the Inquisition, murder - sorely testing the young hero's optimism.

The Republic poses questions that endure: What is justice? What form of community fosters the best possible life for human beings? What is the nature and destiny of the soul? What form of education provides the best leaders for a good republic? What are the various forms of poetry and the other arts, and which ones should be fostered and which ones should be discouraged? How does knowing differ from believing?