Throughout history philosophers have sought to define, understand, and delineate concepts important to human well-being. One such concept is "knowledge." Many philosophers believed that absolute, certain knowledge, is possible—that the physical world and ideas formulated about it could be given solid foundation unaffected by the varieties of mere opinion.

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.

A Treatise of Human Nature is the first work ever published by David Hume, a man who revolutionized our understanding of philosophy. Hume was an advocate of the skeptical school of philosophy and a key figure in the Scottish Enlightenment. He looks at the nature of human experience and cognition, showing that philosophy and reason can only be reflections of our nature.

On Liberty is a book by John Stuart Mill, one of the most celebrated philosophers on the subject of leadership and governing ideals. The book focuses on Mill's philosophy on utilitarianism which is one of his defining principles. The principles of the book are focused on developing a relationship between the ruling authority and liberty.

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?

Both astonishing and prophetic, The Abolition of Man remains one of C. S. Lewis's most controversial works. Lewis sets out to persuade his audience of the ongoing importance and relevance of universal objective values, such as courage and honor, and the foundational necessity of natural law. He also makes a cogent case that a retreat from these pillars of our educational system, even if in the name of "scientism", would be catastrophic. National Review lists it as number seven on their "100 Best Nonfiction Books of the 20th Century".

"The central miracle asserted by Christians is the Incarnation. They say that God became Man. Every other miracle prepares the way for this, or results from this." This is the key statement of Miracles, in which C. S. Lewis shows that a Christian must not only accept but rejoice in miracles as a testimony of the unique personal involvement of God in his creation.

Considered to be one of the most important philosophical works of all time, the History of Western Philosophy is a dazzlingly unique exploration of the ideologies of significant philosophers throughout the ages - from Plato and Aristotle through to Spinoza, Kant and the 20th century. Written by a man who changed the history of philosophy himself, this is an account that has never been rivaled since its first publication over 60 years ago.

Schopenhauer was just 30 when his magnum opus, Die Welt als Wille und Vorstellung, a work of considerable learning and innovation of thought, first appeared in 1818.

Much to his chagrin and puzzlement (so convinced was he of its merits), it didn't have an immediate effect on European philosophy, views and culture. It was only decades later that it was recognised as one of the major intellectual landmarks of the 19th century.

Critique of Judgement was published in 1790 and is divided into two parts, the Critique of Aesthetic Judgement and the Critique of Teleological Judgement. Our ‘judgements of taste’, as Kant describes our aesthetic judgements, have both a personal and a universal function: personal, because we have a subjective aesthetic response to the ‘agreeable’, the ‘beautiful’, the ‘sublime’ and the ‘good’; but also there is a ‘universal’ aspect because our aesthetic response has a ’disinterested’ element. This brings under Kant’s spotlight, for example, the concept of beauty and the perception of beauty.

Immanuel Kant's Fundamental Principles of the Metaphysics of Morals, first published in 1785, lays out Kant's essential philosophy and defines the concepts and arguments that would shape his later work. Central to Kant's doctrine is the categorical imperative, which he defines as a mandate that human actions should always conform to a universal, unchanging standard of rational morality.

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 Problems of Philosophy discusses Bertrand Russell's views on philosophy and the problems that arise in the field. Russell's views focus on knowledge rather than the metaphysical realm of philosophy. The Problems with Philosophy revolves around the central question that Russell asks in his opening line of Chapter 1 - Is there any knowledge in the world which is so certain that no reasonable man could doubt it?

Philosophy of Mind is the third and final part of the Encyclopaedia of the Philosophical Sciences, the collection in which Hegel (1730-1831) offered an overview of his life’s work. Though originally written in 1817, he revised it in 1830, thus providing a finished form the year before his death. Hegel used the three parts of the Encyclopaedia - Science of Logic, Philosophy of Nature and Philosophy of Mind - as a basis for lectures at the Universities of Heidelberg which he joined in 1816, and in Berlin in 1820.

There is a cause, or a reason, behind everything that happens. This is the fundamental view behind the classical proposition the Principle of Sufficient Reason, which, in 1813, Schopenhauer chose as his subject for further examination in his doctoral dissertation On the Fourfold Root of the Principle of Sufficient Reason....