The fugue of Bach, as it is represented, for example, in the forty-eight fugues of his “Well-Tempered Clavichord,” is a contrapuntal or polyphonic form; that is, it is made up of from two to five voices or parts, progressing with complete melodic independence of one another, yet in entire harmony. It is based on, or proceeds out of, a short motif or subject, often but a measure or two in length, but subjected to the most ingenious, varied, and exhaustive manipulation. It has certain structural divisions, and always ends in the key in which it began; yet its form does not, strictly speaking, depend on its sectional structure, as is the case with the song, dance, and sonata forms, but rather on the logical exploitation of the motif. The motif, in a word, is the primary fact of the fugue, the seed from which is germinated all the luxuriant florescent life of the subsequent music.
Since the motif is the animating force of the entire fugue, it is obvious that upon its pointedness, variety, and interest will depend the vitality of the composition as a whole. Bach accordingly spares no pains in the construction of his motifs. Much as they differ in length, expression, and style, all are brimful of interest. Each embodies some striking musical idea; some persuasive or emphatic rhythm, some definite tonal design which either by its oddness or by its utter naturalness and inevitability lays firm hold upon the attention at once, and coerces interest whenever it recurs. Here are a few motifs from the “Well-Tempered Clavichord”:
FIGURE VII.
The variety is wonderful, even in these five subjects; and it will be seen at once how provocative of musical thought they are, like condensed aphorisms, packed with suggestions that send the mind questing through endless vistas of imagination.
As for the further treatment of the fugal motif, the actual formal rules, despite the awe they have immemorially aroused in the popular mind, are few and simple. After the first announcement of the subject by a single voice, it is answered by a second voice, at an interval of a fifth above;[27] then again stated by a third voice, and answered by a fourth. This process goes on until each voice has had a chance to enunciate the motif, after which the conversation goes on more freely; the subject is announced in divers keys, by divers voices; episodes, in a congruous style, vary the monotony; at last the subject is emphatically asserted by the various voices in quick succession (“stretto”) and with some little display or grandiloquence the piece comes to an end. But simple as is this scheme, it gives the composer ample opportunity to develop his theme with the utmost ingenuity, to subject it to the most surprising metamorphoses, and to place it in ever new lights and postures.
