When the idea of an autobiography was suggested to Isaiah Berlin, he reacted with horror, rejecting the idea as a ‘terrible thought […] like walking naked in public’ and adding that ‘I take no interest in myself whatever.’Apart from ‘My Intellectual Path’ and various passages in Personal Impressions (notably ‘The Three Strands in My Life’), Berlin wrote little about himself for public consumption. But even if he had responded to requests for autobiographical pieces, his habit of reworking texts again and again before finally approving them for publication might have led to the creation of a quite new persona. As it is, the best source of information on how Berlin really viewed himself (and on the accuracy of that view) is the constant stream of letters which poured from him throughout his life, and which Henry Hardy and I are editing. Whether handwritten or dictated into a machine for his secretary to type, Berlin's letters to friends, acquaintances, professional contacts and total strangers have the unrestrained spontaneity of his conversation. And as they were frequently despatched without re-reading by their author, what he says about himself has the freshness of first thoughts.

Many of Berlin's letters can be seen as precursors of his academic pieces, as he tries out on friends the philosophical, intellectual and moral positions for which he later argues in public. His dismissal of overriding principles in favour of more pragmatic solutions is a frequent theme; in the mid-1930s he commends Macaulay for a scale of values ‘not consisting in rules i.e. moralistic and irrational & ugly’and by 1949 is ready to argue the position at length: ‘Once principles are applied rigorously absurdities follow from the non-generalizability of the situations which originally suggested the principles. […] one must judge each situation, so far as possible, on its own merits & not commit oneself to campaigns for general principles.’ Sometimes the letters expose the genesis of his intellectual preoccupations. Berlin's diatribes in his letters about the malign influence of sociology and the growing demand for education to be socially useful throw new light on the argument of ‘Political Ideas in the Twentieth Century’.