Henri Bergson (1859-1941) was the leading French philosopher of the first half of the 20th century. Near the end of his life when he was forced to register with the police in Nazi occupied France he wrote: ‘Academic. Philosopher. Nobel prize winner. Jew.’ Time and Free Will, his doctoral thesis, was published as a book in 1889 and attacks and rejects the mechanistic view of causality described in Kant’s version of space and time and proceeds to attempt to define free-will and consciousness by separating space and time.

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.

Matter and Memory, (Matière et Mémoire), published in 1896, was the second book written by Henri Bergson (1859-1941), one of the leading French philosophers of his age. It followed Time and Free Will (1889) and helped to establish him as a major force in anti-mechanistic thought, opposing the trend towards uncompromisingly secular and scientific views. However, when Matter and Memory appeared, Bergson was 39 and had yet to become the hugely influential figure he became in the first decades of the 20th century.

In 1929, Martin Heidegger (1889-1976) published his remarkable book Kant and the Problem of Metaphysics. The Kantbuch, as Heidegger often called it, is regarded by many as a vital supplement to the unfinished second part of Heidegger’s most influential work, Being and Time, which was published two years earlier in 1927.

Karl Popper's THE POVERTY OF HISTORICISM is one of the most important books on the social sciences to have appeared since the Second World War. It is also the work of one of the most original thinkers of the twentieth century, and a devastating criticism of the idea that there are laws of development in history and that human beings are able to discover them. Popper dedicated the book to all those who fell victim to the fascist and communist belief in Inexorable Laws of Historical Destiny

Among the many important historical documents from the Classical world of Greece and Rome The Antiquities of the Jews by Flavius Josephus is one of the most distinctive and characterful. Josephus (37-c100 CE) set out with the clear purpose of telling the history of the Jews from the creation in Genesis to the Jewish revolt against the Romans in 66 CE. Born in Jerusalem as Yosef ben Matityahu, he rose to become a leading participant in the First Jewish Revolt (66-73 CE).

Throughout the twentieth century, The Protestant Ethic and the Spirit of Capitalism was regarded as an important sociological and economic text, continuing into the twenty-first century, when extreme capitalism has continued to come under fire. Weber's work provided a history, from where the profit motive could be ethically justified. Max Weber combined his interests in sociology, political economy and history to give perspective to his analysis. Concentrating principally on the experience of the West, he returned to the time when religion, its concepts and practice, dominated society.

This Leibniz collection contains some of the philosopher’s most important works and ideas, spans three decades and illuminates the fascinating intellectual journey undertaken by him in his quest for truth. A prodigious polymath, Leibniz was a mathematician, philosopher, physicist and statesman and engaged with a sweeping range of ideas and disciplines, striving throughout his life to be at the cutting edge of scientific thinking. These Principal Essays are arranged in chronological order.

Being and Time was published in 1927 during the Weimar period in Germany, a time of political, social and economic turmoil. Heidegger himself did not escape the pressures and his nationalism, and undeniable anti-Semitism in the following decades cast a shadow over the man, but not the work. Being and Time is not coloured by expressions of his later views (unlike other writings) and remains an outstanding document.

In the 21st century, Carl Gustav Jung (1875-1961) remains one of the key figures in the field of analytical psychology - and Psychological Types, or The Psychology of Individuation, published in 1921, is one of his most influential works. It was written during the decade after the publication of Psychology of the Unconscious (1912), which effectively ended his friendship and collaboration with Sigmund Freud.

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 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.

Sigmund Freud (1856-1939) is remembered as the father of psychoanalysis. Civilization and Its Discontents (1930) is one of his key works, written three decades after his seminal book The Interpretation of Dreams. In it he considers the conflict between the needs of the individual acting both egotistically and altruistically in the pursuit of happiness and the myriad demands of civilised society and the ensuing tensions this clash of needs and demands generates.

The Critique of Practical Reason was published in 1788, seven years after Immanuel Kant's major work, Critique of Pure Reason. In it, Kant sets out his moral philosophy - and it proved a seminal text in the history of the subject. He argues that the summum bonum (the highest good) of life is that rather than just pursuing happiness, people should inhabit a moral dimension that enables them to deserve the happiness that God can give. Though much shorter than Critique of Pure Reason, this is the sourcebook for Kant’s ethical doctrines.

The front cover of the second edition of Language, Truth and Logic carried this statement in capital letters: ‘THE CLASSIC TEXT WHICH FOUNDED LOGICAL POSITIVISM - AND MODERN BRITISH PHILOSOPHY.’ It was a bold statement, but the book, first published in 1936 when A. J. Ayer was just 25 and a lecturer on philosophy at Christ Church, Oxford, drew unstinting praise from leading figures in the field, including Bertrand Russell.