This series of 28 lectures was given by Sigmund Freud (1856-1939), the founder of psychoanalysis, during the First World War and first published in English in 1920. The purpose of this general introduction was to present his work and ideas - as they had matured at that point - to a general public; and even though there was to be considerable development and change over the ensuing years, these talks still offer a valuable and remarkably approachable entry point to his revolutionary concepts.

First published in 1930, Civilization and Its Discontents is one of the most influential works of pioneering psychologist Sigmund Freud. Focusing on the tension between the primitive drives of the individual and the demands of civilization for order and conformity, Freud draws upon his psychoanalytic theories to explain the fundamental structures, conflicts, and consequences of society.

Here are three key works by Sigmund Freud which, published in the first decades of the 20th century, underpinned his developing views and had such a dramatic effect on world society. In the uncompromising Three Essays on the Theory of Sexuality (1905), he declared that 'sexual aberrations' are not limited to the insane but exist in 'normal' people to a greater or lesser degree. The three essays are divided between sexual perversions, childhood sexuality and puberty.

This collection of 11 wide-ranging lectures which appeared originally in 1933, was based on lectures previously given when Jung was in the process of absorbing a considerable period of study of Eastern religions, Gnosticism and other religious sources. It was a time, according to the translator Cary F. Baynes, ‘when the Western world stands on the verge of a spiritual rebirth...after a long period of outward expansion, we are beginning to look inside ourselves once more.’

Published first in 1912, Psychology of the Unconscious was one of the most important stepping stones in the development of Jung’s thought and practice. It has a long subtitle: A Study of the Transformations and Symbolisms of the Libido. A Contribution to the History of the Evolution of Thought. This expressed the underlying impetus - a break from the view of the libido and its functions as taught by Sigmund Freud, which Jung had earlier adopted. It was from this point that the two approaches, which came to be known as the Swiss and Viennese schools, emerged.

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.

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".

Nietzsche was one of the most revolutionary thinkers in Western philosophy and Thus Spoke Zarathustra remains his most influential work. It describes how the ancient Persian prophet Zarathustra descends from his solitude in the mountains to tell the world that God is dead and that the Superman, the human embodiment of divinity, is his successor. With blazing intensity, Nietzsche argues that the meaning of existence is not to be found in religious pieties or meek submission, but in an all-powerful life force: passionate, chaotic and free.

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.