But what of the difficulties which such a theory must meet? The most obvious one is the short life of musical works. If musical beauty is founded in natural laws, why does music so quickly grow old? The answer is that music is a phenomenon of expectation as founded on these natural laws. It is the tendency of one note to progress to another which is the basis of the vividness of our experience. We expect, indeed, what belongs objectively to the development of a melody, but only that particular variety of progression to which we have become accustomed. So it is that music which presents only the old, simple progressions gives the greatest sense of ease, but the least sense of effort--the ideal motion not being hindered on its way. Intensity, vividness, would be felt where the progression is less obvious, but felt as "fitting in" when it is once made; and where it is not obvious at all--where the link is not felt, a sense of dissatisfaction and restlessness arises. So it is with music which we know by heart. It is not that we know each note, and so expect it, but that it is felt as necessarily issuing out of the preceding. A piece of poor music, really heterogeneous and unconnected, might be thoroughly familiar, and yet never, in this sense, felt as SATISFYING expectation. In the same way, music in which the progressions were germane to the existing tonality-feeling, while still not absolutely obvious, would not be less quickening to the musical sense, even if learned by heart. It is clear that there is an external and an internal expectation--one, imposed by memory, for the particular piece; the other constituted partly by intrinsic internal relations, partly by the degree to which these internal relations have been exploited. That is, the possibility of musical expectation, and pleasure in its satisfaction, is conditioned by the possession of a tonality- feeling which covers the constituents of the piece of music, but which has not become absolutely mechanical in its action. Just as rhythm needs an obstacle to make the structure felt, so melody needs some variation from the obvious set of relations already won and possessed. If that possession is too complete, the melody becomes as stale and uninteresting as would a 3-4 rhythm without a change or a break. The test of genius in music, of the width and depth of mastery, is to be able to become familiar without ceasing to be strange. On the other hand, if in music to be great is always to be misunderstood, it is no less true, here as elsewhere, that to be misunderstood is not always to be great. And music may be merely strange, and pass into oblivion, without ever having passed that stage of surprised and delighted acceptance which is the test of its truth to fundamental laws.