"... One writes for the acoustical and aesthetic properties of the instruments at hand. And one cannot separate the masterworks of music from the forces and the instruments and the vocal training which is associated with these things."That is to say, whatever instrument is in your hands affects your playing style. He notes that Viennese pianofortes such as Mozart played had a high-velocity action due to their smaller, lighter hammers and that they were wood hammers with leather cushions that emphasized the initial transients. This contrasted them with the English pianofortes with larger, slower hammers that were cushioned with felt as we have now. You can see the difference in his playing technique on this instrument: on a piano with a heavier action you would expect the playing to come more from the shoulders, but this instrument responds quickly and brightly to being played from the elbows and wrists. And Mozart's music plays to the strengths of the instrument.
"...Every instrument wishes to be played in a certain way. And you either learn that, and you get the instrument to sound the way it wants to sound, and then it will do anything for you, or you fight it. And it you fight it, you will loose the battle."Well stated. The point being that an instrument has a range of expression available from it. You have to learn to exploit the instruments strengths. From a compositional standpoint, you can feel this when you are working out a new piece and shopped it around to various guitars. You find that different instruments can either fight or enhance performance of a particular piece. To put it another way, it is a two-way street: your playing can either fight or work in sympathy with an instrument. Be it in the stiffness of the strings or the amount of energy required from the right hand to excite the instrument or the length of a particular left-hand stretch, the character of the instrument plays into your interpretation of the music.