The four books of the Summa contra Gentiles were written by Thomas Aquinas between 1259-1265, before the considerably larger and more influential, Summa Theologica. The purpose of each work was different. Whereas the Summa Theologica addressed the faithful, especially theology students, the intention of the Summa Contra Gentiles (Systematic Exposition Against Non-Christians) was to speak to a non-aligned and even hostile audience. To that purpose, Aquinas presented arguments ‘refuting specific beliefs or heresies.'

Parerga means 'supplementary to a main work', and Paralipomena suggests a further supplement, but these two books were anything but a casual addition to his major opus, The World as Will and Idea. For a start, it was the publication of Parerga and Paralipomena in 1851 which brought Schopenhauer to the attention of the general public, decades after The World as Will and Idea first appeared.

John Locke (1632-1704) was a product of his troubled times: he lived through the English Civil War, the Interregnum, the Restoration, Monmouth’s Rebellion, the Bloody Assizes and the Glorious Revolution. His empirical thinking was very much directed at finding rational solutions to the root causes of those troubles.

Towards the end of his life and his career as one of the leading politicians and orators in Rome, Marcus Tullius Cicero (106 BCE-43 BCE) was exiled to his country house. It was a time of political turmoil in the capital of the empire, caused by the power-grab of Julius Caesar. In the quiet of the countryside, Cicero began to write on philosophy. In On the Ends of Good and Evil, he set out to consider three major traditions of Greek philosophy - Epicureanism, Stoicism and a branch of Platonism.

Though David Hume (1711-1776) is now best known for his role as a prominent philosopher of the Enlightenment rather than an historian, it was his momentous six-volume The History of England that really brought him national attention during his lifetime. Not surprisingly, this volume covers the greatest number of years; the increasing availability of historical record allows for far greater detail. But Hume is still fascinating as he discusses the passage of time from Julius Caesar, through the advent of William the Conqueror and the Normans, to the death of King John in 1216.

Zen Buddhism is often said to be a practice of mind-to-mind transmission without reliance on text—in fact, some great teachers forbid their students to read or write. But Buddhism has also inspired some of the greatest philosophical writings of any religion, and two such works lie at the center of Zen: The Heart Sutra, which monks recite all over the world, and The Diamond Sutra, said to contain answers to all questions of delusion and dualism. This is the Buddhist teaching on the perfection of wisdom and cuts through all obstacles on the path of practice.

Aristotle’s Nicomachean Ethics and Eudemian Ethics represent, in many ways, the Western classical springboard for the systematic study and implementation of ethics, the optimum behaviour of the individual. (By contrast, Aristotle’s Politics concerns the optimum blueprint for the city-state.) It is in the hands of each individual, he argues in these books on personal ethics, to develop a character which bases a life on virtue, with positive but moderate habits.

From the moment of its publication in 1748, The Spirit of the Laws proved to be a controversial work provoking widespread interest. Within three years it had been translated into various European languages - and was swiftly added to the List of Prohibited Books by the Roman Catholic Church. It is a remarkable book, a potpourri of observations and comments ranging far and wide over the social activities of mankind and it exerted a great influence on political leaders in the following decades.

In his autobiography, David Hume declared unequivocally that this work, An Enquiry Concerning the Principles of Morals (1751) is "of all my writings, historical, philosophical, or literary, incomparably the best." In it, Hume takes the discussion away from traditional attitudes where either rational or metaphysical issues govern moral principles. Instead, he introduces the human factor, introducing the sentiments and passions inherent in human psychology.

Two contrasting reflections by Aristotle which cover very particular ground. In 'On the Soul', Aristotle presents his view of the 'life essence' which, he argues, is possessed by living things whether plants, animals or humans. Not a 'soul' in the generally accepted Western use of the term, this 'soul', he says, is a life force that is indivisible from the organism that possesses it.

The Travels of Marco Polo is the classic account of Marco Polo's journey to China from Venice, and his discoveries as an emissary to the great Kublai Khan. Polo explores everywhere from Baghdad, Armenia and Russia to the Caspian Sea, the Gobi Desert and the small fishing villages of China, describing the geography, architecture and customs of these exotic places.

As philosophy professor Taylor Carman explains in his helpful introduction, Edmund Husserl (1859-1938) was the founder of modern phenomenology, one of the most important and influential movements of the 20th century. Ideas, published in 1913 – its full title is Ideas for a Pure Phenomenology and Phenomenological Philosophy – was the key work. It is arguably ‘the most fundamental and comprehensive statement of the fundamental principles of Husserl’s mature philosophy’.

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.

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.

Proclus - or Proclus of Athens, as he is sometimes known - is widely and rightly considered to be one of the most significant later Neoplatonist philosophers. At age 40 (c.437 CE) or so, Proclus became head of the revived Plato’s Academy in Athens. In his role for the next 50 years, the unmarried Proclus worked hard, combining effectively the roles of administrator, teacher and writer. Astronomy, ethics, mathematics, physics, theology - Proclus tackled all of those topics that together fell under the umbrella of philosophy in his time.