"There is an important difference between an advance in science and achievements in the humanities. A great musician consumes intellectual capital, he does not supply it, or at least it is usual for him to consume more than he creates. It has been impossible to use the motto theme of the Fifth Symphony after Beethoven used it. In science, on the other hand, the situation is the other way round. A breakthrough invariably opens up more new problems to be solved. A Newton or an Einstein may leave the world with a century or more of clearing up to be done."