The act of composing is the act of fixing those limits within which the performer may move freely. But the performer's freedom is - or should be - bound in another way. The limits the composer sets belong to a system which in may respects is like a language: it has an order, a syntax and a meaning. The performer brings out that meaning, makes its significance not only clear but almost palpable. And there is no reason to assume that the composer and his contemporaries always knew with certainty how best to make the listener aware of that significance.
-in discussing his opposition to the "historical performance movement". Rosen is an American pianist and musicologist. To see posts about his works, check the book list.