Some years ago I lent a copy of Isaiah Berlin's volume of essays on his contemporaries, Personal Impressions, to a friend and neighbour, the psychiatrist Bob Gosling. When I later asked him what his own personal impression was of the book and its author, he confessed: ‘I did get rather tired of all that praise.’ There is certainly a lot of praise in that collection, and it is no doubt partly a matter of taste how one responds to the kind of sustained enthusiasm for humanity in all its teeming multiplicity that was one of Berlin’s hallmarks. But Gosling's response also misses a point. The prominence of praise was quite deliberate. Berlin much preferred celebration to denigration, on the whole, and his main purpose in the pieces that make up that volume is to see the point of each of the very various people he writes about – to ‘accentuate the positive’ , as the song has it – and to convey it to the reader, which he duly does, often to spellbinding effect.

When Wolfson College asked me to compile a book about Berlin to mark the centenary of his birth, it seemed natural to turn the tables on the master eulogist and invite a number of those who have encountered him closely, in person or on paper, to provide their own personal impressions of the man, and of the point of his life and work. So there is much praise here too. Indeed, one might issue a warning to readers, along the lines of those announcements that precede radio or television programmes liable to offend their audience: ‘This book contains strong laudatory content throughout.’ Nevertheless, I think there is also in these pages a sufficient lacing of detachment and reservation to placate Gosling's shade. And even those who find accumulated eulogy indigestible cannot fail to be struck by the power Berlin had to elicit personal love and intellectual and moral admiration in almost every, if not quite every, quarter. The degree to which he did this is surely remarkable and exceptional by any standard, and deserves examination. What manner of man was this? This is the question to which this collection is addressed.