It is interesting that these two biographies should have appeared at a similar time. Each concerns a writer with some call on our attention, Arthur Koestler, the fierce freelance enemy of the Nazis and Communists and Isaiah Berlin, the urbane, patrician aesthete from All Souls. They knew each other too, as their biographers make clear. Koestler found Berlin too "donnish" and would certainly have viewed him as insufficiently anticommunist; and Berlin did not like Koestler's effective abandonment of his Jewish heritage. It is impossible, in any case, to imagine their being very close friends. The hard-drinking, macho, promiscuous Koestler and the reticent and fastidious Berlin would surely have jarred on each other in a very short time.

That their personalities were so different might perhaps not have mattered particularly. They might still have been drawn to each other spasmodically. The extrovert Koestler was very friendly with the preternaturally private and shy Orwell. Koestler was always drawn to people with distinctive characters, whether that distinction was based on power, wealth or fame. He often associated with people whose views he detested, provided they had some marks of distinction. Sartre was one such, and the dreadful A.J. Ayer another. Indeed Koestler had that sort of parvenu inferiority complex which drew him to people he thought socially superior even if he despised them intellectually. While he and Berlin could never have become intimate, he would have undoubtedly seen the latter as socially distinguished. Koestler with his horrendous Middle European accent would, for example, have been much impressed with Berlin's mastery of upper class English dialect and speech conventions.

Moreover much united these two men. Both were immigrants to this country, both were more or less Anglophile. Both were famous, both were Jewish, both were multilingual and prodigiously talented. Yet Koestler has always lit my intellectual candle as effectively as Berlin and his various concepts of liberty and his evocations of German romanticism have not. It is hard to put one's finger precisely on the reason. As Mr Ignatieff makes clear, in an indifferent text, though better written than Dr Cesarani's, there were extraordinary events in Berlin's life too. Who else at the height of Stalin's power was in Russia, to meet Pasternak and Anna Akhmatova? Who else could claim to have been confused with another I. Berlin, greater indeed I opine than he, the American songwriter? For most of his life Berlin knew everyone who was anyone in British intellectual and artistic circles.

Why then does Koestler so fascinate and Berlin so weary the spirit? Their biographies changed nothing for me. Dr Cesarani writes very badly, a manifest victim of the bad English teaching which hit our schools in the 1960s. Worse, his biographical judgement is poor. He wants to define Koestler by his Jewishness. This simply will not do. Koestler remained a central European Jew to the end. But we must take a writer's word for it when he or she says something serious. Koestler said for forty years that the concept of Jewishness was anthropologically and historically meaningless and mischievous. This is nonsense; but it is what he believed. At the very least, however, it should make us look further than mere extrapolations from the little Jewish boy from Budapest, which is the rôle in which Dr Cesarani casts him.

In fact Koestler is defined by his anticommunism. In the volume of superb autobiography entitled The Invisible Writing, in 1953, less than a decade after losing much of his family in the Holocaust, Koestler declared roundly that Communism was the most inhuman political system ever devised and the greatest threat to our civilisation that had ever existed. Everyone is against Nazism. It goes with being human. Koestler thought that Communism was just as hateful or worse, and found it intolerable that all intellectuals did not excoriate the Communist menace.

Koestler stands alongside Orwell as the greatest of the anticommunists. That is how history will remember him. By contrast one would have to ask of Berlin's shade: just what was his problem? Nothing stands out in Mr Ignatieff's book, though the sections on Russia are the most memorable, suggesting genuine pity and love on Berlin's part.

There are other things. There is Koestler's superlatively imaginative prose-writing. His combination of literary talent, especially his flair for metaphor, and his unusual scientific knowledge, gave Koestler powers of prose-writing beyond those of anyone else in that brilliant emigration from central Europe which marked the middle years of the last century. Popper, Hayek, Polanyi, Mannheim, Kolakowski - none of these could write like Koestler. By contrast Berlin's soothing and elegant prose rolls effortlessly off the page and equally painlessly out of the mind. Is this because he had no central problem? Was Maurice Cowling's obituary remark that Berlin wrote no big book because there was not one in him, a correct judgement?

Maybe the difference between these two men is spiritual. When it comes to moral issues, we know little about Berlin and it is even conceivable that there is not much to know. He thought our condition ineradicably ambiguous morally, split as we are between incommensurable choices. Mr Ignatieff makes it clear that this was a private, careful man, one not very active sexually. In the general moral and intellectual sense he has great admirers, like John Gray, who was a friend. Equally I have known people at All Souls who detested him. For those like me with no personal experience, it is hard to come to a decision. Mr Ignatieff's glossy book does not help.

We have to use the word spiritual again. Dr Cesarani shows effortlessly enough what a shit Koestler was. He was a lecher, even a rapist, according to his biographer. He seems to have forced at least one girlfriend into an abortion, which sits badly with the man who always claimed that the mechanistic aspects of the Enlightenment were unacceptable to him, that the nature of things is written in an invisible writing of which in rare moments of grace we are vouchsafed a glimpse. He dismissed Judaism, unfairly, as mostly just a set of archaic dietary laws; and he was too proud to see that Christianity was the true answer for his restless genius and troubled soul.

What by contrast can we say of Berlin? Mr Ignatieff shows him as in a quandary when his beloved father was worrying that death might be the end of life. His son held precisely that belief. Mr Ignatieff says that Berlin hated the callow anticlericalism of the Voltarian Enlightenment. Why then did he come across so often as an Enlightenment sceptic. In one television interview I saw soon after his death, he said that he saw no evidence that God exists. That sounds pretty definite to me. Give me the suicide and the lecher rather than the polite sophisticate articulating his nihilism on the edge of the grave. Some will call it brave. It certainly recalls the Roman patricians. Asking for trouble is what I call it. Koestler was a sentimental rogue, who spent years of his life in the wastes of parapsychology. Fortunately these will not cancel out his superb contribution to the theory of despotism and his ingenious writings in the philosophy of science. In any case, at least he had the merit of recognising a mystery when he saw one. In this matter at least the rogue has it over the patrician every time.

Dennis O'Keeffe