Ferrucio Busoni was a genius. To say that he played the piano in an extraordinary way is merely to state the blindingly obvious.

I recall a concert when he played Liszt's The Legend of St Francis of Assisi Preaching to the Birds in a way that revealed the greatest depths in the work; listening to it, I tried to pin down what he did that made it seem so extraordinary. It wasn't until I had heard it three times that I realized he had managed the incredible tour de force of giving to the trills scattered all over the page the same nunber of notes - but this kind of feat didn't matter. Above all, you sensed a unity in his interpretations. But on the other hand, he was a demon for invention; was he as great a creator as he was a genius himself? I leave the question open.

He was not greater than Beethoven. He was not greater than Mozart. He was among the greatest. He played in a singular way, with the air of composing as he played; and I think that his achievement would have been greater if he had not tried to make Mozart say what he, Busoni, saw in him - which he liked to add.

Hence the necessity for watchdogs in matters of interpretation. In any event, Busoni's articulation was perfect, and came not from the astonishing evenness of his technique, but above all from his prodigious sense of rhythm.

One mistake that should never be made is tampering with the tempo. What gives a piece of music its unity, its essential character, its dominant character? It is the underlying pulse, which must be respected even when other liberties are taken and one uses what is called 'rubato'. The rubato of a really serious musician doesn't break the unity of the beat. Take a record by Toscanini, put on your metronome and you will see that everything is in marvellous accord. Liberty can only exist within the scope of a regular, severe, immutable pulse.

- Bruno Monsaingeon, Mademoiselle: entretiens avec Nadia Boulanger, Paris 1981. English translation © Robyn Marsack 1985