Biographies are not often a pleasure to read. Too many are badly edited and bulked out with a mass of irrelevant detail, pseudo-psychological mumbo-jumbo and insights that are suspect to say the least. The heavier the weight, the less enlightening they are in helping us to understand the mind of the person they portray.

Ian Thomsons Primo Levi is biography at its best. The author has, with great sensitivity, told the life story of a modest, decent but complex man who was also a fine writer. Levi wrote with simplicity, clarity, a gentle humour and, above all, a deep understanding of the human condition.

The challenge that Levi faced was how to remain a compassionate and civilised human being in inhuman circumstances. In 1943, aged 24, he was rounded up by the Italian SS and sent with 600 other partisans and Jews to a prison camp in northern Italy. In 1944 he was transferred to Auschwitz, where he spent a year in terrible privation. He escaped the gas ovens because his profession of chemist made him valuable to his captors and he was assigned to laboratory work. When the Russians swept victoriously into Germany in 1945 he escaped the forced march to Berlin because he was in the prison infirmary with scarlet fever. The SS guards were instructed to kill all patients but they ran away without doing so, and again Levi was spared. He arrived home in Turin in late 1945 after a long and difficult journey, experiencing at first hand the chaos of post-war population shifts and territorial land grabs.

Levi was not an adventurer, nor a hero in the conventional sense of the word. He was a quiet, studious Italian youth who graduated from Turin university in 1941 and who intended to go on to study physics. Like many other young Italians born into secular Jewish families, he considered his Jewishness simply as the feeling that I shouldnt eat salami, but I eat it all the same.

The proclamation of Mussolinis anti-Semitic laws changed all this. When Levi needed to become an interno to research his graduate thesis, only one of his professors, Nicol Dallaporta, had the courage to defy the legislation and allow him to work in his experimental physics institute.

Levi graduated with first class honours but his diploma was marked member of the Jewish race, effectively barring him from further study. Eating salami was not possible any more.

He had difficulty finding work and had to use a false name and depend on the goodwill of his employer to hold a job. He worked first in a factory in Turin extracting nickel from asbestos, then in Milan for a Swiss chemical company on a cure for diabetes. In Milan, he lodged with a relative who made her large house available to friends: Catholics, Protestants and Jews working in various professions under false names. They were an intelligent, joyous group, all strongly anti-Fascist.

As the Russian front and the American entry into the war drew the noose tighter around the Axis powers, these young people became more active. In the spring of 1943 Levi joined the Action Party because of its cautious liberal socialism and its intellectual integrity. One of his first tasks was to smuggle clandestine propaganda to the mountain villages outside Milan. It was during this mission that he was rounded up.

The experiences that followed were the inspiration for his first book If this is a man, and his account of his return to Turin after the Liberation became The Truce. He saw courage and compassion in men and women of different faiths, different social levels and different nationalities, including his German captors.

He wrote If this is a man rapidly, submitting it to a publisher in early 1947. Einaudi, managed by Cesare Pavesi, turned it down on the advice (later admitted to be an error) of Nathalia Ginzburg. It is too soon, they told Levi. In October 1947 a small, almost bankrupt publisher printed an edition that sold only 1,500 copies. There were few reviews and only one, by Italo Calvino, of importance. It was not until the late 1950s that Einaudi published it in Italy, and in 1958 Orion in the United States published an English translation.

Levi did not become a writer living and communing among other writers. He continued his work as a chemist in an industrial plant until he retired in his 60s, writing in solitude and receiving visits by those who admired his books and his philosophy. He married, had a family, looked after his ailing mother and lived in the family apartment in Turin. He re-visited Germany and kept in touch with his fellow inmates, in particular the bricklayer Lorenzo Perrone, a civilian worker at Auschwitz who put himself in mortal danger by sharing his meagre rations with Levi.

He struggled with the question that must affect all survivors of the facist regime: Why did this happen, how could human beings do it, and can it happen again?

He did not want to be pigeonholed as a Holocaust witness. He insisted that humane and inhumane behaviour were not a matter of race and this drew him much abuse from right-wing Jews. In 1982 he publicly condemned the raids on Sabra and Chatila in Lebanon authorised by Israeli prime minister Menachem Begin and the then defence minister Ariel Sharon as bringing shame on Jews, and was subjected to threats and curses. In 1985 he was criticised in New York as being a dilettante unable to understand the significance of the Holocaust.

Levis death in 1987 from a fall (perhaps it was vertigo, perhaps it was suicide) has been attributed by some to the deep depressions he suffered in his later years, by others to the anti-depressant medication that he took. Holocaust survivor and Nobel peace prizewinner Elie Wiesel believes that Primo Levi died in Auschwitz forty years later. Others wonder if he died because he could no longer face a world in which human beings still have not learnt that inhumanity should not be tolerated. Thomson wisely concludes that if Levi did commit suicide we must accept that the suffering of those who kill themselves is private and inaccessible.

Primo Levi by Ian Thomson. Vintage, February 2003.

Available at English-language bookshops in Rome.