Unfinished Dialogue by Isaiah Berlin <br/> Political Ideas in the Romantic Age by Isaiah Berlin

We need Isaiah Berlin's subtle and commonsense appreciation of liberal values now more than ever. As Berlin noted, values are often in conflict and there is no incorrigible proposition by which they can be reconciled. It may well be that sections of Islam see no value in the rule of law or in pluralism, but that is the reason why we should understand the roots of our liberal society. It is a more effective defence of our values than enhanced techniques of interrogation and the 90-day detention of suspects.

Two new books, Unfinished Dialogue, based on Berlin's correspondence and conversations with a Polish academic, Beata Planowskya-Sygulsksa, and Political Ideas in the Romantic Age, a collection of Berlin's writings on the origins of liberal thought, which later were the basis of his most famous work, Two Concepts of Liberty, have been published this year. Both are from the stable of Henry Hardy, supremely diligent editor of the scattered Berlin oeuvre.

For Berlin experts these two books offer new insights into the development of his ideas, which were occasionally contradictory but always very human and personal. For the lay reader they are full of the most extraordinary common sense. One of Berlin's favourite quotes was from the 18th century Bishop Butler: "Things are what they are; why should we wish to be deceived?" As Berlin saw it, there is no final reconciliation, no overarching explanation, no march of history, no heaven, no political science, no natural rights. We have to deal with the here-and-now. Berlin particularly loathed the idea, used to justify great tyrannies, that we are living in a condition of false consciousness and it is only the state that can bring us to our true selves

His disarmingly simple question, the central question of political philosophy, was "Why should any man obey any other man or body of men?" This is first found in the early essays which form Political Ideas in the Romantic Age, and turns up again in later work. It was a real question, because his formative years coincided first with National Socialism and then Communism. Human values, he argued, are facts in themselves and the important thing is that human beings create values; they do not discover them, pace the Bible or the Koran or Marx. So we should distrust any leadership which claims to order our liberty and our lives according to a master plan. We are not talking here of hospital league tables but rulers who believe that there are greater truths which exist independent of human experience. Above all, Berlin was intrigued by real lives, by the human condition. I find the following passage both eloquent and intensely human, qualities rarely found in professional philosophers:

"Man is incapable of self completion, and therefore never wholly predictable; fallible, a complex combination of opposites, some reconcilable, others incapable of being resolved or harmonised; unable to cease from his search for truth, happiness, novelty, freedom but with no guarantee of being able to attain them, a free, imperfect being capable of determining his own destiny in circumstances favourable to the development of his reason and his gifts."

It is a love letter to human nature and by implication a profound repudiation of oppression by ideologues. Berlin loved the work of Ivan Turgenev and he believed he shared Turgenev's temperament: Turgenev was fascinated by the radicals in mid-19th century Russia, but unable to act himself. Berlin in his Romanes Lecture on Turgenev's Fathers and Children speaks about Turgenev and the radicals, but he is also writing about himself:

"He shared their hatred of every form of enslavement, injustice and brutality, but unlike some among them he could not rest comfortably in any doctrine or ideological system. All that was general, abstract, absolute, repelled him: his visions remained delicate, sharp, concrete, and incurably realistic. Hegelianism, right-wing and left-wing, which he had imbibed as a student in Berlin; materialism, Socialism, positivism, about which his friends ceaselessly argued, populism, collectivism, the Russian village commune idealised by those Russian socialists whom the ignominious collapse of the left in Europe in 1848 had bitterly disappointed and disillusioned - these came to seem mere abstractions to him, substitutes for reality, in which many believed and few even tried to live, doctrines which life with its uneven surface and irregular shapes of real human character and activity, would surely resist and shatter if ever a serious effort were made to translate them into practice."

This is purest Berlin, expressive of his deep and instinctive beliefs and revealing of his character. Both in his dialogues with Beata Polanowska-Sygulska and in Political Ideas in the Romantic Era, we find that Berlin's understanding of liberty and how best to preserve it, come down in the end to a rejection of all that "is general and abstract". He gave up philosophy when he realised that it was largely abstraction, a substitute for reality. Instead he turned to the history of ideas, examining de Tocqueville, Mill and Rousseau; Constant, Kant, Hegel, Bentham, Hobbes and many Russians, including Alexander Herzen in his search for a sense of what liberty means.

In the fascinating dialogues conducted towards the end of his life with Beata Polanowska, he explained some of his influences and how he came to his famous division of positive and negative liberty, and his realisation that values "collide and clash and cannot be reconciled". Yet when in l958 he prepared to deliver his revolutionary lectures on liberty, he was tormented by the possibility that what he had written were "sonorous platitudes".

In fact, Berlin gave the world a wonderfully nuanced understanding of human behaviour and human nature, and a wholly new way of looking at the pretensions and follies of totalitarian regimes. Strangely, the explosive nature of his ideas took some time - as Henry Hardy remarks - to detonate in the world outside Oxford.

Berlin's passionate engagement with the world led him to the understanding that what matters are the real effects of ideas on people, with their "irregular shapes of real human character". He was very fond of Kant's quote that nothing straight was ever made of the crooked timber of humanity.

One size will never fit all. This is the meaning of pluralism.

Justin Cartwright's new novel, 'The Song Before it is Sung', will be published by Bloomsbury in February