The great disadvantage of this admirably concise and organic structure proved in the course of experience to be a certain monotony and rigidity. As movements became longer and more complex, the division into two sections, embodying but two keys in spite of momentary excursions to more remote centres, came to seem rather constricting. There was a dearth of variety about it, and a tendency to obviousness. The element of contrast, of adventure far afield, was somewhat lacking. Composers accordingly worked out, of course unconsciously, a more various but equally organic scheme of design--ternary form. In ternary form the first section is practically identical with that of binary form; but the second, instead of “marching down again,” makes the contrasting tonal centre it has reached but a starting-point for still further excursions. It modulates freely, using to the utmost the privilege of admission to all the keys of the gamut that music owes to Bach and his system of equal temperament; it plays with the theme, subjecting it to the modes of development we have already studied; it indulges in all sorts of pranks and whimsies, departing as much as possible from the set formality of the first section; in a word, it endeavors to establish a complete contrast with what has gone before, and while never violating logic, to get away as far as possible from the beaten track, from the rut of routine. Then, after this interregnum of variety, comes the third section with an emphatic reassertion of regularity, presenting once more the subject as at first, and in the tonic key, vindicating the unity of the movement of the whole, and rounding it out to orderly completeness. Splendid examples of this splendidly organic structure are most of the preludes, gavottes, bourrées, and minuets of Bach’s suites. In the suite, then, as it was practiced by Bach and other seventeenth-century composers, we see operative a constantly broadening application of the use of expectation and fulfilment, in the interests of organic structure. Applying to artistic music those methods of metrical and harmonic form that had long determined the growth of folk-song and dance, the composers of this period gradually learned to make even wider and more intricate syntheses of their materials. So skilfully did they avail themselves of the relations between contrasting harmonic centres that they were able eventually to write whole movements as firmly organic, as deftly coordinated, as a vertebrate animal. By the ever-extending use of thematic variation and of free modulation, they made their pieces as various as they were systematic. And at last, in ternary form, they established that succession of statement, contrast, and reassertion, which seems even to-day the last word in the philosophy of general musical structure.