FIGURE VIII.
Practically all the possibilities of developing a motif were exploited by Bach in his marvelous fugues. The development of the motif means, in the most general terms, the repetition of it in forms sufficiently like the original one to be recognizable, yet sufficiently unlike it to be novel and interesting, to exhibit it, as has just been said, in “new lights and postures.” Now, since the identity of the motif depends on the fixed metrical and harmonic relations of its constituent tones, it is obvious that variation of it will have to consist in slight alterations of these metrical or of these harmonic relations, or of both, managed with such skill that they do in effect vary, without disintegrating, the motif. Our next task, then, will be to describe the chief means, both metrical and harmonic, by which the motif, in the hands of Bach and of all his successors, is modified without being destroyed.
Mere repetition, of course, is not, strictly speaking, development, however efficient it may be as a means of building up musical structures. With the repetition of the motif at a different place in the scale, however, such as is used in the “answer,” we have a true development, though an elementary one. Here all the metrical and harmonic relations of the motif are kept intact, at the same time that the bodily shifting of it in the scale throws upon it, so to speak, a new light. This will be felt at once by any musical person who will play over attentively the two subjects and answers of Figure VIII. A much more radical change is effected when the motif is changed from major to minor, or vice versa, or presented in some key other than the dominant and more remote, or presented with new harmonization. Still, even in such cases, the metrical and fundamental harmonic form of the subject remains unaltered.
In the device called “inversion,” much used by Bach, we have an essential change. The metrical form of the subject, remaining unchanged, ensures recognizability, but the harmonic relations, while remaining identical in respect of size, are exactly reversed in respect of direction; in other words, the subject is turned upside down. A few examples will explain this better than many words.
In Fugue VIII, Book I, W-T.C.,
becomes