Ray Monk is professor of philosophy at the University of Southampton and is the author of Ludwig Wittgenstein: The Duty of Genius, and Bertrand Russell: The Spirit of Solitude. His most recent book, Bertrand Russell: The Ghost of Madness 1921-1970, focuses on Russell's relationship with his son, John.

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"The following list is unashamedly 'unbalanced'. Of the 10 books listed, four are by a single philosopher: Ludwig Wittgenstein. I make no apologies for this. In my view, Wittgenstein towers above all other 20th century philosophers to such an extent that it is surprising to find any books not written by him included in such a list."

1. The Principles of Mathematics by Bertrand Russell

This is the nearest Russell came to writing a magnum opus. In its original conception it was to have been the book that established the truth of "logicism", the view that mathematics is nothing more nor less than a branch of logic. Unfortunately, this aim was scuppered by Russell's discovery, late in the book's development, of a paradox that threatened his whole system of logic. The book contains a tentative solution to this paradox, but, more than that, it established the lines of thinking that would dominate the philosophy of mathematics throughout the 20th century.

2. Logic and Knowledge by Bertrand Russell

If one wants to know why Russell is regarded as a great philosopher, one should read this collection of his early essays. In particular, his 1905 paper, 'On Denoting', is arguably his greatest contribution to philosophy. It is in that paper that Russell expounds his famous Theory of Descriptions, a theory that has had a decisive influence on the style and content of the entire analytical tradition. In 'On Denoting', Russell set subsequent philosophers a great challenge: the challenge of seeing through the grammatical structures of everyday language in order to identify the logical structures that lie beneath them. In one way or another, most subsequent analytical philosophy can be seen as an attempt to rise to this challenge.



3. Tractatus Logico-Philosophicus by Ludwig Wittgenstein

This is the only book Wittgenstein published in his lifetime, and is universally acknowledged to be a masterpiece. Though it has now received 80 years of commentary, there is still no settled view as to what, exactly, Wittgenstein meant by the numbered oracular pronouncements of which the book is composed. It has been read as a logical positivist tract, a work of religious mysticism and an exercise in Kierkegaardian irony. Wittgenstein himself insisted that its central point was to distinguish that which can be said in language and that which has to be "shown". Perhaps because of its opaqueness, it is a book that grows in fascination the more often one reads it.



4. Philosophical Investigations by Ludwig Wittgenstein

This is, in my view, the greatest philosophical book ever written. Compared to Tractatus Logico-Philosophicus, it is easy to read, but its true meaning is no less difficult to assimilate. At its heart is an assault upon the tendency, pervasive in almost all philosophical thinking, to "look for a substance whenever one sees a substantive". Thus, we ask: "what is the mind?" "what is consciousness?" and so on, without realising that our puzzlement will not be dispelled by finding something that is the mind, consciousness, etc. This is because the source of that puzzlement does not lie in the absence of such "substances", but rather in the assumption that there must be such things in order for the words we use to have any meaning. Wittgenstein's assault on this assumption is rich and many-faceted and has wide-reaching implications for all philosophical thinking.



5. Remarks on the Foundations of Mathematics by Ludwig Wittgenstein

Philosophical Investigations was left unfinished at the time of Wittgenstein's death. His original intention was to include in it his investigations into mathematical concepts, which, he thought, mirrored the investigations into psychological concepts that now form the bulk of the book. Remarks on the Foundations of Mathematics brings together the manuscript volumes from which Wittgenstein would have drawn the remarks on mathematics he had wished to include in his magnum opus. Mathematicians and logicians have been shocked by the radical tendency of Wittgenstein's remarks on mathematics, and philosophers, for the most part, have ignored them. But they seem to me to be essential reading for anyone interested in understanding Wittgenstein's approach to philosophy.

6. Culture and Value by Ludwig Wittgenstein

In his philosophical manuscripts Wittgenstein would often write paragraphs in code. These were usually either personal remarks or wide-ranging reflections on culture and society. A selection of the latter is included here, which provides an extraordinary insight into the spiritual and cultural preoccupations that lie, unspoken, at the root of Wittgenstein's philosophical work. Among other things, what they show is the degree to which Wittgenstein's whole work was animated by a deep dislike of the "scientism" that characterises 20th century intellectual life.

7. The Crisis of European Sciences and Transcendental Phenomenology by Edmund Husserl

This is Husserl's last work, left unfinished at the time of his death in 1938 and written when he was in exile from Germany, having lost his academic position because of his Jewishness. It represents a deep and moving attempt to respond to the crisis facing the intellectual world in the 1930s as a result of the rise of barbarism. Husserl connects this barbarism to what he regards as a pervasive misunderstanding of human reason, a misunderstanding he tries to correct through his notion of the Lebenswelt ("lifeworld"). The sciences, he insists, can be given meaning only if they are founded on phenomenology. Whether he is right or not, it is impossible not to regard this as a deeply serious attempt to deal with an issue of monumental importance.

8. The Bounds of Sense by PF Strawson

Peter Strawson is one of the very few 20th century British philosophers capable of writing elegant prose, and The Bounds of Sense is quite beautifully written. What it presents is an engagement with The Critique of Pure Reason, determined to strip from Kant's seminal work its obscurity and its flirtation with a priori psychology. I have always found its last chapter on geometry particularly provocative, presenting as it does a sophisticated and penetrating argument that provides a partial defence of Kant's views on the subject, views that Russell thought he had demolished half a century earlier.

9. An Autobiography by RG Collingwood

There are surprisingly few good autobiographies by philosophers. They tend to be disappointingly superficial and to give little sense of what it is like to be in the thrall of philosophical perplexity. Russell's My Philosophical Development is an exception to this, and so too is Collingwood's marvellous work, which, though militantly "internal" and intellectual (one gains almost no sense from it of what Collingwood's personal life was like), conveys vividly the forces which drove Collingwood's philosophical thinking. Collingwood's contributions to philosophy have been disgracefully under-valued, but this should not put anybody off reading this gem of a book.

10. Metaphysics as a Guide to Morals by Iris Murdoch

Based on a series of lectures, this provides a sweeping overview of the philosophical concerns that guided Murdoch's life and work. The Platonism she espouses is unfashionable, and with good reason, but what makes this such a compelling book is the sense it gives of the attractions of Platonism for someone with refined literary and artistic sensibilities. The arguments in this book may lack rigour, but what commands respect and attention is the way Murdoch conveys the sense, felt by many, that there has to be a metaphysical basis for our ethical judgments, otherwise we are forced to navigate our way through life without a rudder.