I was first introduced to Isaiah Berlin in the green room of the Queen Elizabeth Hall after one of my Beethoven recitals – in 1975, I think. Dana Scott, the American mathematician and logician, and his wife, the pianist Irene Schreier, had brought him along from Oxford, where Dana was lecturing at that time. With Irene as a four-hand partner, Dana sometimes played pieces of his own composition, which sounded roughly like the Viennese waltzes of Lanner.

A few days later I saw Isaiah again at Lord Drogheda’s. His voice, still strong and firm, was booming across the dinner table with great incisiveness and speed. A friendship soon developed, and my wife Reni and I would often spend time with Isaiah and Aline, either at Headington House, the Berlins’ lovely Oxford residence, or at our London home, or in their Ligurian refuge at Paraggi, or at Plush Manor in Dorset, where we entertained Isaiah and his friends on his eightieth birthday.

Before the birthday dinner, I gave a concert in the adjacent church, a recital that included Schubert's B flat Sonata, whose Andante sostenuto I was to perform again at Isaiah's memorial service in Hampstead Synagogue in January 1998 – the movement had become one of Isaiah's favourites. A few years previously, he had listened to a programme of Schubert's last three sonatas that I gave at Stowe School, and it seemed to have persuaded him of the greatness of this triad. He must have heard Artur Schnabel, the revered pianist of his younger years, play some Schubert; but the cumulative impact of the three works seemed new to him. It was as though part of his enthusiasm for Rossini and Verdi (Isaiah was a regular patron of the Pesaro Festival) had gradually been transferred to Beethoven and Schubert. There was something childlike about Isaiah's appreciation of music. When a piece stayed strictly in time, as in some Italian opera, he delighted in beating the rhythm on his thigh. (Isaiah greatly valued Toscanini.) But his nostalgia for musical naivety, memorably expressed in his essay on ‘naive’ and ‘sentimental’ music (in Schiller's sense), did not mean that he was unable to enjoy the different, more complex rewards of the great ‘German’ composers.

Isaiah's special interest, however, was opera. To please him, it needed opera producers who served the composer, not themselves.